I'm not sure I see that, as TDE relies on Qt3 which hasn't been supported for some time (current version is Qt6), and whilst the MATE desktop started with GTK2 (also unsupported, thus was maybe ~equivalent), it was ported to GTK3 which is still in maintenance mode (current version GTK4) and thus does receive some support.
I do see MATE as in a better position than Trinity.
I've hum'd and har'd about responding to this thread, whilst I'm on the Lubuntu team, as no doubt many on this site will know, but on this site I'm representing Ubuntu or Ubuntu-MATE and not Lubuntu!. I'm aware of talk at various levels about the need to create a documented flavor removal processes, some teams struggling with lack of contributors thus flavor teams being difficult to reach at critical times, I had a question asked of me (from Ubuntu Release team member) relating to Ubuntu MATE 24.04.3 ISO which took me ~20 mins to notice/respond to, but Martin Wimpress had already responded within ~2 mins so far faster; to me that reflects well on Ubuntu-MATE.
To me, be it I'm logged into a MATE desktop session, Xfce desktop session, or LXQt desktop session on my current Ubuntu questing system, it's still a Ubuntu system to me that I'm using. The desktop maybe tweaked by different teams (or I have GNOME from Ubuntu Desktop team on this box too) but the system is still Ubuntu.
If the Ubuntu-MATE team was to close up, I could still use the MATE desktop, as much of what I get comes from upstream Debian sid anyway. If Xubuntu closed up, again as most of that also comes from Debian sid I'd notice little difference there either (if you watch, you'll regularly see Xubuntu devs talking about uploads to Debian sid on Xubuntu [IRC] development channels; update there & the one upload benefits both Debian and Ubuntu!; which MATE team members have done too). Of the desktops I've mentioned; I'd notice the biggest difference if Lubuntu closed up, as the Ubuntu repositories regularly have newer package versions than are uploaded into Debian sid, plus the [Lubuntu] team makes more Lubuntu specific changes (compared to Xfce/MATE) in my opinion anyway.
If anyone was worried about Ubuntu MATE closing up; they can still use Ubuntu with the MATE desktop, just as Xubuntu users could still use Ubuntu with Xfce desktop, etc.
To me Ubuntu MATE is really just a Ubuntu system used with the MATE desktop on it anyway.