Their first problem is asking for a cover letter. I’ve applied to hundreds of jobs while looking, you think I’m going to hand write 100+ cover letters, customized for each and every job? Hell no.
Depends on what job I'm applying to, if it's a job I really want for sure I'll be writing an awesome cover letter, e.g. when I tried and got very close to working for an amazing NGO that would've sent me and my family to Polynesia you bet I was giving my best in the application. If I'm applying for a batch of faceless companies XYZ then yeah screw that.
The real issue is that every single application requires you to provide a CV and cover letter, only to then make you re-enter all of the info from those into their likely terrible hiring software that will force you to sign up. Then the majority ghost you.
So yeah, while I agree it's not worth writing a custom cover letter for every job, I'd say CVs are worse. As you are pretty much forced to anyway as you re-enter everything over and over despite providing a copy of your CV.