It's not necessarily just the servers. TSR is quite an old version of vBulletin which has been suped up and modded beyond all recognition. It's kind of like a PS2 that is somehow running Warzone.
I would guess that the problems are the same old same old - TSR is yesterday's social media run on yesterday's software and is somehow still clinging to life. They've tried absolutely everything to try and monetize the site and the only thing that works is selling a fifth of the screen to google ads- and because traffic isn't what it was, there isn't the revenue or the willpower to migrate to something new. I would suspect that they're scared of doing so in case they invest heavily and the TSR just fails.
On those servers, tho - there's too much junk clogging up the forums due to poor management. They closed MHoC angering a whole bunch of people and made some lame excuses, and yet they have hundreds of pictures of Ainsley Harriot and other pointless spam games. That's all space on the servers just being wasted.