Because in the 80s the choices were few.
In the 90s I had the refrigerator sized rack set up.
By the 2000s and especially now, there are all sorts of builders making cool high gain stuff JUST FOR METALHEADS! This kinda gear didn't exist during my heyday in the 80s, and I certainly didn't have the disposable income then that I have now. My first ENGL made me wanna try them all. Same with the Herbert and Diezel. Then VHT. I eventually kept my favorites from each brand. Once I got my first weirdo amp, I realized there are other people making cool high gain amps and wanted to try them too. Then it got to the point that it was more of a hassle to sell and ship an amp than it was worth.
There have been unmitigated failures along the way. The REVV Generator. Diamond Nitrox. ISP Theta head. I never bonded with the Mark IV. Never really like anything Fortin designed either. Countless others that came and went. But a couple of good ones got away just to try something else...and now I refuse to let that happen again. All my keepers make me happy when I get to plug them in. I obviously have favorites. But I still wanna try amps I haven't got a crack at. It's not like you see a Wizard Hellrazor or a Hermanson at Guitar center in the boutique room...you gotta buy one to really know what's up. And 10-20 minutes on one at an ampfest will wet your appetite for sure, but you wont really know until you live with it.
In some cases, a best bro will know you well enough to say "I know you and your style of playing. You should get this amp.". Juggernaut Mike kept telling me to get an Ultralead. And for damned sure, he was right. Mailman Dan was right about a couple of amps I got from him and still have, mainly because they remind me of him at this point. Some have great stories, some have great tones. Some are just so different than everything else that I just dig them. Some were custom built or modded and signed for/to me. One was borrowed from me for a major concert and signed by the artist to me. How could I possibly let that go? I flew from Texas to California and back to buy an amp from a builder. The story on that one alone still makes me smile every time I plug into it.
But most importantly, I don't have to sell them. So why should I? I have zero debt and an insanely great credit rating. Plenty of money in savings. OK...I admit that my storage situation is out of control, as a few of my friends here can attest. But they all sound great to me and make me happy just knowing I have them. My guitars and amps all have a story. Those stories may only matter to me, but they are almost as important as the stuff I inherited from my mom and dad. Once you get old, memories are the most important things you will ever have.
But in all honesty, that is just how I justify my gear to myself. The rest of you can lick my taint.