I wasn't even aware that certain retailers can completely bypass rules of EU or country level quality standards. I thought those were enforced already.
Thing is/was (don't know if something changed over the last year) for example for temu, that you as the customer are also the importer. Thereby you as the importer are being held accountable for the product meeting the necessary quality standards (e.g. the ce sign). If the cheap electronics from Temu explode and your house catches fire, the cost is all on yourself.
Afaik, TEMU is only a broker between hundreds of exporters and the customer (who is also the importer). Banning the exporter of basically useless, they just reopen under a new name.
I assume they'd still have to register a new account with temu and lose their reviews? Being diligent about that seems already like a good start, at first glance...
If they'd ban Temu, which they currently don't seem to have legal ground for, Temu would just stop printing their logo on the labels. New sender address, done. It's not like the follow laws now anyway. They also lie about the value of packages to avoid paying import taxes.
It might work, but the EU doesn't have a central entry point / organisation handling the mail so the legislation needs to be airtight if you want this to be effective.