My read is that there's a lot more competition now. The M1 just isn't as competitive with (for example) the NR200 being so similar, 1/2 the price, and produced by a major manufacturer/system integrator.
It's not the SFF case that I'm using now, but it's the one I used the longest and was certainly the most versatile. If I hadn't decided to build my first custom loop in the Meshlicious, I'd still be using my M1 today.