Probably none of the above.
I doubt the failure rate is higher, but I imagine the user base is much larger now than in the past, and the ease of complaining/sharing your experience is DRAMATICALLY higher, especially if it was a bad outcome, everyone shares it which makes it seem much more likely than it is.
I don't think that acrylic tanks are worse long-term than glass tanks, and I think they've both been used for the last 30 years pretty consistently, proportionately (that's my impression, but I've only been reefing for ~14 years). Acrylic is always somewhat niche, and the majority of tanks have consistently been glass.
I don't think anyone is struggling with applying/curing silicone. Perhaps manufacturing has changed, or the volume of tanks being produced by tank builders have changed which might lead to lower quality than historically, or that they're not "overbuilding" as much as they used to, but I wouldn't attribute that explicitly to "struggling with applying/curing silicone".
The only massive tank failures I've seen or heard of were when the old JBJ nano cube 24 gallon tanks used to crack and leak because the glass was too frail in the beginning (I had one of those tanks, was the second owner, moved it around the southeast of USA in my back seat, sometimes 1/4 full of water, and never had a problem). There are a few threads of tanks leaking or bursting, but I only know one person who has had that experience, and his was a custom-built magnificent 375g, built by a very reputable builder who has been doing it for ~40 years, and somehow one of the side panels blew out about a year into having the tank. Giant disaster considering how advanced this hobbyist is, his stocking, and level of involvement in the hobby, but I guess it happens. I still think it's extremely infrequent.