The reasons for no MATE 1.28 on Trixie are discussed here: "Mate 1.28 on Debian" · Issue #646 · mate-desktop/mate-desktop · GitHub.
The issue seems to be a lack of time that the developers have; the shifting sand of GTK3 is partly to blame (this is why developers complain about GTK3 and API/ABI breakage).
GTK2 reached EOL in 2020 after reports of about 4 years of focussed effort to develop GTK4. If GTK5 is developed and released on a similar schedule, then we've probably got at least a couple of years before GTK3 reaches EOL.
LXQt seems to compare quite well to MATE in terms of being a lightweight traditional desktop. I've decided it's not realistic to expect consistent themes across apps; Qt, GTK, Electron (which I hate) are never going to cooperate in terms of look and feel. So, basically, my priorities boil down to 1) low resource utilisation, and 2) easy to navigate for me (I'm probably not going to change to, say, a tiling window manager any time soon).