It's already publicly funded for most of the budget. You can scrap ticketing systems/gates and use the conductors somewhere else in the economy.
It won't happen, not because it's more expensive, but because governments like to keep track off movements.
When electric cars were fairly new, free chargers were fairly common and people would horrendously abuse them. They would leave their cars plugged in past the time the charge was complete. So the people who wanted to charge their batteries every minute their car was idle spoiled it for the rest, even people who desperately needed to charge.
So I think of the same thing wrt public transportation. I believe NYC had enough subsidies that they could make their subways free, but the behavior of outliers like people who would live on the trains spoiled it for the rest.
(but yes, tracking)
You can buy any ticket in cash at the automatic ticket machines. I don't think it's that, the government has enough cameras to track you in general, they don't really need ticket records.
Especially considering that tracking the general population by phone is much easier and efficient.
But yes there's quite a lot of overhead in the ticket system, it would certainly be more efficient to just fund everything from general taxes.
> governments like to keep track off movements.
This doesn't make sense, train subscriptions don't make this possible. I have a train subscription but am only checked 1 times out of 10. The other 9 times no one knows where and when I got on or off the train. (Except if they examine the cameras in the stations.) A single ticket also only has a date, no time. And until a few years ago, conductors still 'cut' those, with an 'analog' tool; it's only recently they started scanning them.
It is possible that is the long-term goal. Getting there may be incremental, and providing a 49EUR ticket could be one step in that direction. Convincing people to do "all free" may only be possible by first agreeing to a lower-cost ticket.
Given that situation, I definitively would have mostly preferred better rather than cheaper public transport, but apparently everyone has succumbed to a frenzy of "free, free, free, gimmie, gimmie, gimmie!"…
[1] E.g. Hessen is right now still cutting its public transport budget in order to balance debts caused by Covid, Baden-Württemberg has cancelled a stated goal of increased service quality (a goal of providing public transport at least every half hour even in rural areas and every 15 mins in urban areas) before it ever really got started because it now has to finance its share of the 49 €-ticket and doesn't want to spend even more [2], etc. etc.
[2] I don't want to be too ultra-harsh on the latter – compared to a low point in terms of financing in the mid-/late-2000s, things have definitively improved and the state government is definitively spending more on public transport again, but clearly not limitless amounts more.