Starting to feel old, because apparently I am the only one who remembers how sl spawn was switched off on Anctoville and replaced by spawn halftracks back in 2.25. God that sucked.
Anyway, regarding SL spawn and Rally points, the thing is this: RPs (and spawn vehicles) solve some problems and cause others.
The main advantage is that the SL does not have "the weight of the world" on his shoulders and doesn't have to stay alive at all cost. This also eliminates the stupid SL roulette that popped up in the meta a few years ago (believe me, people didn't always do that shit).
However, it does little to fix SLs hiding, instead of looking for some camping SL you are looking for some stupid box. At least when hunting an SL there is some actual player interaction, since you have to fight him, instead of knifing some radio. A spawn vehicle or rally point is also much more easily camped. Sure, they can be deactivated when enemies are close, but I can already see Sturmflim laying down with his MG 40 m away and just waiting for people to pop up. Way harder to do with a squad leader who might shoot you. This is already happening on the pacific maps, where people just camp the landing boats and people spawn in because there is no indication of if they are safe or not.
Lastly, the SL spawn has the advantage of being more "idiot-proof", which is important since the average community member has an IQ close to room temperature. Instead of complaining "MOVE!!" People will complain about squad members not staying close so they can't put down a rally point.
So all in all, the advantages are not big enough to justify completely changing a system at this late point. Really, the ideal solution would be having sls be able to spawn on each squad member, but that is impossible.