I think that this is the one. Tell me your satisfaction with Maya or 3ds Max
Actually, Maya v1.0 came out in 1998. That makes it 22 years as of this coming February. That’s not including the carry over user base from PowerAnimator and Wavefront. Maya is basically just a Frankensteined rewrite/fusion of the two. Its core design and use in production goes as far back as 1988.
And that comes across as a shock… how? 
Look. If you own a legacy version, Autodesk doesn’t care about you. They’ve got your money. They’re interested only in new money. That’s why they’re pushing subscriptions, to maintain that flow of new income. Autodesk isn’t in the business of making software. They’re in the business of selling it. They’re all about milking that cash cow.
First they ditch perpetual license sales in favor of subscriptions. Then they stop supporting activation of perpetual licenses older than “x” years, effectively forcing you to subscribe if you want to continue using. (The side consequence here is that these perpetual license are now not so perpetual.) Next they create an indie version so crippled and incompetently executed that you’re forced to go with a full subscription if you want an actual Maya experience.
If it seems as if they’re not doing much about backwards compatibility that’s because they’re not. They don’t care. Autodesk does everything in their power to push you toward subscriptions and thus paying in perpetuity. That they even provide ANY updates beyond general compatibility is secondary. They could go without any major features for years and not care because their business model has shifted.
Contrary to popular belief, Autodesk no longer sells software. They sell subscriptions. Knowing that, I wouldn’t hold my breath waiting for enhanced backwards compatibility. As they push more users to subscriptions, the cries for such functionality will quiet. Anybody still left on an old version or with old files will be told to either use non-ma/mb export, 3rd party conversion solutions, or just suffer.
Good luck with replying to their “how can we help” type threads too. In recent months, they asked for input and were told about the inadequacies of the Indie version. Their response was a “fake” indie pricing structure. That brought the full version to indie users a low price… for only 12 months. The fine print was that they’d forced into full subscription pricing via auto-renewal. Of course, they’ll tell you that it was a limited promotion thing, but that’s not exactly how it was promoted. They touted it as a real solution to indies. Sleazy and further proof of what they really sell - subscriptions.
I honestly and genuinely feel for you. I do. I hold a valid Maya subscription myself and it’s only out of necessity, not legitimate desire. If I had any inkling that they had the end users’ best interests at heart, I’d tell you. Personally, however, I think that they’re far more interested in our money than our input. Because they’re the de facto standard, they think that they’re the only game in town and can screw users six ways to Sunday. We’ll see how long that mindset lasts though. An anti-ADSK/subscription sentiment seems to be growing these days.
As far any lost/old files you may have, my condolences. I’ve been there. I’ve got a lot of old work in outdated, unsupported formats. At first, I practically cried. I just had to throw my hands in the air and accept that I’d never get that stuff back again. Autodesk users aren’t alone with this problem.