I originally thought that about the safeties, but I do have a few Sigs without them and they do sell the S&W models with and without safety. I have a Shield 2.0 without. My Sig 320 has a safety which means it's not at all modular unless I am cutting out the safety notches in the grips (that infuriates me) and my 365 has a safety as well. I think if it has a safety, trigger pull can be "normal" If it doesn't, it has to be 10 pounds. This is when it's sold. There is no law (yet) saying it can't be modified after purchase. I did put an Apex spring kit in my Shield. It's like spinning the roulette wheel here trying to guess what they are thinking and why.I wonder if it's because Glock doesn't make any with manual safeties (like the 1911's, etc). Maybe Mass. doesn't think Glock's trigger safety mechanism is "Safe" enough. Just a thought. I've seen many manufacture's websites, have different models Indicating Mass. compliant, Cali. compliant, etc. Never really looked into these models, as I was fortunate not to live there.
I think Glock just wasn't going to modify their weapons for MA.