I own and use an OG 909 - I guess you could say that I’m one of those techno producers that OP is asking about.
The simple and main reason is that I already have it. I bought it almost 20 years ago for 800 bucks and had to eat instant noodles for a month to be able to afford it at that point in my life. Even back then, they were already considered classics and appreciating in value, though not to the stratospheric degree we see now. I’m certain that there are a lot of long-time users that are in the situation as I am - they bought the machines back in the day when they were still affordable.
Another contributing factor for me is that I have a personal connection to my particular instrument - 2 decades’ worth of using it means that I have a lot of memories and experiences attached to it. Call it sentimentality, but my 909 serves as a reminder of countless gigs and hours of sweat equity in various studios, and I love it for that.
And of course, there is that the 909 is “That” sound and “That” functionality. For me personally, nothing compares to it, aside from the legit replicas like DinSync’s RE-909. Roland’s own TR-09/TR-8S is mostly there, Jomox has it’s own thing going on, the RD-9 sounds and looks like a wish.com idea of a 909 and sample libraries, while great, are like looking at photographs - snapshots, if you will.
But yeah, this is all really my personal take on it, speaking as an owner of the OG.