They are cheaper and come full of spyware preinstalled by manufacturer and carrier.
Customer see the price advantage, everyone else see the data harvesting (including Google). Everyone benefits in selling cheap Android phone.
Now you would be pretty stupid to buy 1k€ Android phone like Samsung ones because they still come with preinstalled and privileged Samsung, third party and Google spyware.
For instance, my s23 had 3 preinstalled meta app. 2 systemized app, 1 was Facebook client.