I really don’t understand why not every subway shows the next station on the screen instead of warning messages and other stuff. (And a marker for side the doors will open)

I don't get why ads are prioritised over travel information.

For at least months in my city, the screens in buses have been showing a "broken image" icon as part of their ad cycle. I'd much rather know about the next stop.

It's very simple: Transit in many places is underfunded. Travel info screens cost money to install and maintain. Ads, on the other hand, make money.

Ads make money, but not that much. I'm not convinced they are enough to be worth the bother. To have ads you need to pay people in sales to sell them, people to install them (now that this is electronic it is easier than the old paper days, but you need a more expensive tech person to keep them working). At best they are 5% of your gross budget, so not very significant and they often hard harmful to your riders.

Transit in the US seems to be constantly on a starvation diet budgetarily speaking so I'm not shocked small sums of money get chosen over options that would be better for their users.

Starvation diet? You should see how much NYC MTA spends, it’s a feast compared to even the rest of the anglosphere

The MTA is a huge outlier but still gets less money for upgrades and upkeep than they need. They limped along for years on extremely outdated train tracking infrastructure and are just getting around to doing updates that needed to be started two decades ago.

They get way more than they need, it’s just burnt on unions, pensions, and consultants

I will literally volunteer my time to canvass for anyone who runs on busting NYC public sector unions

Can you show actual evidence of that. Compare NYC spending to comparably large other systems?

Building and operating are different things.

What often happen is a a company comes into install and maintain the displays for "free", on the proviso that they can display ads and keep most/all of the ad money.

5% of a transit authority's budget would be a lot of money! Advertising made £158 million for Transport for London in 2019, much less than 5% of their budget.

Ads just make money out of people, why not cut off the middleman?

I assume it's because the person deciding what goes on the screens is some manager somewhere. They probably just don't really thing about it.

Also doesn't help travelers who aren't too familiar with English - I always wonder how many NY-bound tourists have stepped off the train at "Newark Penn Station".

I take the train every day in NYC. Around half the time the train is brand new and has nice displays that even show you where the stairs are located in each station as you pull up. The other half the train is from the 1960s and has no information whatsoever. So yeah this app will definitely be an upgrade over peering out the window to read the station names. Even the trains with displays are occasionally wrong/not working.

Even better, they have a thing called a "window" which is transparent and you can look out on the platform and see the sign posting the station name.

This assumes you aren’t riding a packed train with people standing wall to wall in front of seated passengers. Being a shorter than average person also can make this a challenge.