The CV gets you on the desk, the cover letter gets you in the room, and your interview gets you the job.
Your CV really should be as brief as possible, while the cover letter allows you to address some specifics more directly. It's purpose is to make the employer want to even read your CV, rather than skim it.

My sister was a recruiter for many years - if you didn't have a cover letter, you didn't make her cut, let alone the employer's.

Getting a job takes effort, time, takes selling yourself long before you get to meet anyone. It is about making your piece of paper stand out above all the other pieces of paper. Taking the time to do that is valuable, but if you are looking for a pat on the back from every employer you apply to for taking the time to write a cover letter, you will be sadly disappointed every time.
Keep going and don't take everything so personally. There are probably 50 other people applying for each position you are, and they all can't get personal attention. Doesn't mean you won't get there in the end or that the person on the receiving end doesn't appreciate you took the time to wrote a *proper* application.