For sure, it's very difficult to RF in a tiny car with a tall child who doesn't like to cross their legs, needs the seat reclined, and a tight budget necessitating using the existing seat or stretching only to a cheaper seat, and two tall parents. If you have everything like that then it's likely to be tricky to get it to work and it might ultimately not.
But if you can compromise on one of the things, usually the size of the car or the budget for the seat, but also possibly things like the positioning of the seat (e.g. amount of leg room, recline, fitting in middle or front seat, DC one in front of the other) or the recline of the front seats, then it can work. Or you can at least RF until say age 2 if not age 4. Yes there are scenarios where it won't work at all, but I think you can't have everything. People change their car all the time to make more space for DC in general, not only to fit RF seats in. We changed the Swift because we couldn't fit the buggy and a week's shopping into the boot at the same time. And you don't need a car to be gigantic to fit RF seats in, a medium sized car is usually fine. Most extremely tall people don't drive extremely small cars in the first place, and DC usually have long legs or need recline, not both at once (although some cheaper seats can only be fitted reclined).
People do often assume that RF seats take up a lot of space, but if they are more upright they don't need to. We had a Joie 360 Spin (which is the smallest spin seat but not smallest RF seat) in a Suzuki Swift and I didn't have to have the front seat in the most forward position. I found it took up less room than the baby seat, which was much more reclined.
I totally understand and defend "It didn't work with the specific seat we had and we didn't want to research and source a new one when we could just FF" but it is a bit frustrating to see repeated suggestions that RF is frequently impossible unless you have a stretch limousine because that's just not true IME. You would be surprised what can fit if you are willing to spend a bit of time and yes sometimes a bit more money, which I appreciate is not always an option (I would never suggest going into debt for a car seat, especially if you already have one.)
OTOH someone said about a safety gap for FF and that is misleading as well, because the gap is measured from a different part of the seat and is usually only relevant for sports cars where the front seats literally overlap the back seats. It's also only for the legal standard, and not usually instructions for the user, although it is good practice to move front seats away from FF children if possible. I don't know of any RF seat which actually fits within the 50cm gap used in testing for an R129 FF seat. Sometimes a FF seat fits where a RF seat does not, and sometimes a specific seat fits FF where it does not RF, and it's not unsafe to do that necessarily. Generally though if you are breaching the 50cm gap you'll also be squashing the FF child's legs.
OTOH if space is tight, arguably it may be safer to RF because if there is any potential for forward rotation, a RF seat forms a barrier between the child and the seats in front, reducing the risk of head injury. Most seats are allowed to lightly touch the front seat, just not to be wedged up tightly against them. Older seats were designed to do that, but they are no longer sold.
Gallery of ERF in small cars, just for interest, although it's old now: http://erfmission.com/you-cant-rear-face-in-small-cars-debunking-myths-4/