Reliability is absolutely an issue that turns lots of people off - Just yesterday I had to switch to a different line in chicago bc of a delay. But to say that the "large physical size of the US" has allowed aircraft to out compete rail is disingenuous. It is so because it ignores the reality of strong city pairings for rail corridors and such line of thinking doesn't often take into account the boarding process' impact on total journey time. A 45 minute flight is going to require you to get there an hour early for security processing and boarding. You don't just show up 5 minutes before the plane takes off, yet that reality is true for the choo. Even then you still need to offboard, stop by baggage to get your goods and really hope they didn't lose them and have them unpacked in a few minutes. These bottlenecks just do not exist for rail. You get on in the city and get off right in the city. 10 minute taxi to your hotel and bob's your uncle. You simply cannot say the same for any metropolitan airport (Except metro ports that have a dedicated line from the airport to the city center). It won't be viable everywhere but that's not the point. The point is to remove the systemic barriers that prevent market competition where it can thrive (precision rail scheduling in many areas has made it physically impossible for freight to yield to passengers) and to provide reliable, predictable transportation not to the whims of traffic or those who can afford to purchase a vehicle.
Good transit utilizes the best modes for the best routes and this is why high speed rail is really starting in cali and the texas triangle - It's always gonna be faster for rail between two urban areas right next to each other than it is to fly, despite the fact that flying is far more common between such city pairs when people want to avoid driving or need to be there in the city center fast.
I'm far from an expert but I know for fact the United States has many cities that could be covered by HSR that are closer or the same distance as Tokyo -> Kyoto (one of the first HSRs); Keep in mind the shinkansen route is separate from the commuter route and only has a couple of stops. It's not like they reused significant portions of commuter rail, they built a new link.
I'll leave some reading here for more info because there's a lot of worthwhile knowledge to try and understand in projects like these:
CityNerd - Urban planner guy who knows a thing or two about transit
City Pairings for HSR by 2050 - More about city pairings, which is specifically worth focusing on for HSR bc that's how lines get started
America was quite literally built on the railroads. We take for granted the interstate highway system and don't realize its exorbitant cost, but if we had given rail even half the attention we gave the interstate since its inception rail would certainly be competitive. The interstate is national, so why not the rails too? It's not like CSX actually has to compete with BNSF - they don't serve the same area and are inherently monopolies. A business in Montana wanting to use rail for freight has to use BNSF because they're the only freight rail operating and owning lines there. For Denver you're stuck with UP for the same reasons. Most areas are lucky to have a duopoly, and anywhere there is competition is area that has several rail lines merging together, which also makes it perfect for transit.
Per Amtrak (Pg 2, 2021 Report Card) freight rail caused 900,000 minutes of passenger delay across all lines, and in 2023 (Through April, Host Railroad report pg 4) the major freight carriers were responsible for 67.8% of total delays, despite freight being legally obligated to yield to passenger trains most major operators generally ignore that law (Pg 2, Amtrak 2021 report).
So what's the point? Trucking companies don't get to clog the interstate and force passenger cars to yield so deliveries are faster. Passenger planes don't yield to FedEx/UPS/Amazon and circle above landing strips so freight planes get to land first. As a society we don't generally desire to systematically degrade the quality of transit, but we do so for rails because we're conditioned to believe that they are outmoded and just don't work for passengers. If that was true, no where in the world would they be used. Europe and Asia do in fact have more, higher density population centers but this fact does not preclude the capability of passenger rail in America, and we shouldn't believe in this logical fallacy that rail is outcompeted or out moded because of density. China is an interesting example, in that they too have a massive geography that is nearly as varied as America, and not every single city is inherently massive and super dense. Of course being a command economy makes it easy to do infrastructure projects but the viability of those projects doesn't change just because a different government is involved. While we were buying into the hype of hyperloop and slowing down California's HSR project, they built a solid 1000km+ of HSR where there originally was not.
We can do it, in many places HSR is very competitive, and it is economically viable. There does in fact exist a sweet spot of transit, long neglected in the market, where driving is just a bit too cumbersome, but taking a plane isn't any faster.
Of course, I'm just a radical who hates driving and loves trains because of the freedom to goon around with my friends in the city and bar hop without having to DUI or spend $45 on an uber.
