I think "solid" is a relative thing. People weren't comparing the M to the F, which until recently was unavailable except for second-hand units with compromise

I think "solid" is a relative thing. People weren't comparing the M to the F, which until recently was unavailable except for second-hand units with compromise layouts and weird interfaces. They were comparing them to the value-engineered rubber dome they were selling for $14 at the Office Supply Hut. After like 2015 or so, when firms like Ducky and Filco began to bring appealing, consumer-focused MX-switch boards to market, the M becomes just one choice among many. There's also the more subjective angle: people like specific key feels. I like the Model M sound and feel product, probably better even than Model F (too tangy). People will put up with a lot of rubbish for a better feel.