The goal isn't to have one account/offer/trial per person, the goal is to ward off bots and spammers who are going to misuse your service. Since they know they are doing that and they know they could be held liable for what they do, they use sketchy disposable email addresses.

My sites and apps have a blacklist and we don't allow email accounts from those. It's just me running this thing. If I had the security and engineering workforce of even a mid-sized tech company, I wouldn't have to do this. Alas.