I suspect they’re still used for outbound scam calls/texts (and maybe inbound too), and probably gray-market voip-pstn interfaces in countries that make int’l voip interchange expensive.

Some cool stuff on aliexpress with 128 SIM card slots and 8 or 16 gsm radios where you can program your choice of imei.

As a Canadian with crappy cellular coverage, I’ve dreamt of having a couple French SIM cards that I could mail to France every so often so it looked while I wasn’t 100% roaming just to have a cheap unlimited data plan with cheaper int’l calling.