I'm surprised - not just by Train Simulator, but also by smaller games like Melty Blood, Gas Station Simulator and Potion Craft selling as well and better than proper games like Deathloop, Minecraft Dungeons, NBA 2K22, Hot Wheels and Life Is Strange TC... It would be quite interesting to see what made Train Simulator reach that spot, being a very old, very niche, badly received game that's no longer in active development, and somehow outselling hyped games like Deathloop.
If I had to guess I would say that it goes well on release because all of us players know we can get a better deal by buying the game as a bundle.
People keep saying Train Sim's niche, but people seem to underestimate how large of an audience it has. For example the expired Humble Bundle from 2020 shows 77,000 people bought it, and the one the year after had 44,000 sales. Obviously those are way cheaper than they'd normal sell, so it's probably not high in terms of revenue sure. Between that and the Steam Charts it shows there's a large audience with at least a mild interest in this stuff. With that said it also goes to show how poor player retention is when TS clearly pulls in more buyers all the time, yet so few are sticking around and playing it. Honestly I believe if DTG had stronger commitment for quality control and enhancements to the sim it could've been up there at least with the flight sims in terms of player count.
Actually, veterans do remember to wait a few additional months to pay 5€ per route (or a bit more for Deluxe). I agree, the game has potential, I tried TSW and it's pretty, most of my Steam friends are sharing shots from there (and similarly prettier games) but nothing beats the relaxing and versatile nature of TS. Even if it's bit of a niche hobby and many assets are clearly dated and overly reused. I also guess a lot of people only buy a few routes a year because they don't play much. So 5-10 per route is about the deal for them. I have a sneaking suspicion that the lack of updates is a mix of unwillingness to poke old code and that of dedication, resources, willingness. They literally didn't do anything noticeable this year but changing the sort order of workshop scenarios (now newest first instead of oldest). All the while they did mess up a few things over the past 2-3 years, but refused to even acknowledge it. So it's very clearly not even 1 FTE on it. In any event, no huge complaints, game works for me with a few annoyances (main thing is aggressive panning in headphones, as well as ambience cutting out badly, oh and weather, bright white winter nights and yellow dawns) and has plenty of content to enjoy what works.