It's how they make money. It's also how radio stations have income and are able to stay on the air. Without commercials, bills don't get paid, and neither do the people who work for them or own them.
As far as watching shows, advertisers pay the producers of the shows, the station owners and networks, or internet platform to have those commercials on there. Without that, there would be no income or profit. People need to be paid for their work. Producing and presenting shows and movies isn't free. The payroll they put out is huge, providing jobs for a lot of people. When you hear of a program unexpectedly getting cancelled and people voicing concern about all the staff, they are doing so because there are now a lot of people (with families) out of work. Besides payroll, there are also a ton of other expenses involved for sets, clothing, makeup, production and film equipment.
When watching something and you begin to feel upset about all the commercials, consider how much you paid for the show. You may have a service bill for cable, satellite, internet and streaming, but that is for the service, not the individual program. The shows themselves are free to you.
If you don't like commercials, you can mute them, or take advantage of those moments to get something done or get up out of your seat to stretch your legs.