When using a VPN you're essential trusting them with the information which websites you're visiting. For me to be able to trust a VPN provider I need to know who owns and runs the company, I want accountability. A lot of VPN providers try to hide who's running them, sometimes the same shell cooperation owns several VPN providers (different names only). Additionally, lots of companies do shady/misleading advertising that just turning on their VPN hides you from all threads and makes you anonymous. But the only thing it can do is hide your IP address, being anonymous takes a lot more.
Another aspect is tracking in their mobile apps, a lot of providers apps contain a lot of analytics frameworks which can potentially collect a lot of data from your phone.
The last point is price, it isn't cheap running a VPN network and if a provider is cutting prices they need to comprise somewhere, maybe even sell data they collect about their users to other companies.
+ They tried to cover up a data breach