Who cares about unethical labour practices, about the environmental cost, about legitimate designers having their IP ripped off or that these places happily sell your data on when you can get 100 colouring pencils 20p cheaper than you can in home bargains.
But it's not 20p. It's often £10-50 which really adds up if you're buying loads of everyday household stuff that you need to buy anyway (hair clips, hair bands, socks, duvet protectors, hats, gloves, storage containers, stationery etc). Again, people's shopping habits are different but I only use Temu for boring household necessities that I have to buy anyway. I don't care which brands these are, they just need to be functional.
Regarding ethical labour practices, read my post above. Chinese factories do not employ child labour because they are all open to visitations from Western contractors and in close competition with each other. They would have to secretly maintain a child labour room whilst having an open showroom for visitors, which is ludicrous. If one factory is rumoured to be using child labour, or other illegal practices, they would be tipped off instantly by their competitors who want their contracts. It's an egocentric and racist POV to state that all factories in China use child labour when it doesn't make any economic sense on a basic business level.
A similar logic works with the claim that they steal your bank details. If you bought from Temu once and had money stolen from your bank, then you would never use it again. Like any business, they want returning customers so it's in their best interest to get you shopping repeatedly and spend more money than what they could possibly "steal" in a single transaction. Temu is a marketplace similar to Amazon and the money goes to individual sellers. It's not outside the realm of possibility that a few bad players do misuse payment data or are simply unlucky and get hacked. But on the whole, they do not take cash from your bank account as a lasting business model.
Designers have their IP stolen at all levels. There were several high profile cases of Topshop and Zara stealing designs, usually created by third party agencies. Aliexpress has been offering stolen IP work for 10+ years, and it's been around much longer than Temu & Shein. Counterfeit and IP theft is a huge problem but it's been around longer than the app and will pop up elsewhere even if Temu gets banned. AI also steals artists work. It's possible to prompt AI to create work "in the style of" any artist and the resulting image will technically be entirely copyright free. So in a few years, companies who want free imagery will all do that instead of outright reprinting existing work.