They're in the category that, while they theoretically can be used by skilled investors, anyone offering them to retail punters is up to no good. Because those punters are going to lose money to them hand over fist.
I'm not sure if you're writing from the UK or US, but while the latter has a more stringent 'Accredited Investor' qualification (skilled or wealthy, applied and granted) - and actually flat out doesn't allow CFDs anyway (options are much more common & are retail available) - in the UK this just amounts to a KYC type form where you tick that you understand the risks; they also have to tell you (I assume, because they all do) the percentage of customers that lose money trading them on that platform (typically ~75% from what I've seen).
But they're not 'up to no good', you may not like it, but this is allowed and fully above board. If you search 'HL' and get 'Trading212: shares & CFDs' that's a bad search result, but it's not a scam, they genuinely and legitimately offer that, and compete with HL (which doesn't offer CFDs except through some kind of tie-up with IG).
They're in the category that, while they theoretically can be used by skilled investors, anyone offering them to retail punters is up to no good. Because those punters are going to lose money to them hand over fist.