This is to prevent abuse from bots, spammers, hackers, and other things malicious on the Internet. Having a valid credit card means you are probably a real human being
Do you mean understand as in "understand the architecture, structure and the domain" of the project worked on? Are you implying working for 5 hours a month only on a project is not enough for these? Is that what you are saying?
Offering a free service without any kind of barrier would be ridiculous. It is not unknown that free services would ask you for a credit card. For example, website hosting, at a lot of places would ask you for a credit card, even on a free plan. This is to distinguish between bots, scammers and spammers and real human users.
It is a free trial if it is time-limited. Like 30 days, or 2 months. It is not a free trial if it continues forever. I never said it is 5 hours for the first three months or anything like that. If 5 hours is enough for you(and you would be surprised there are many sites that need nothing more than that, just to keep running), then it will be free forever
There are so many websites and apps, that can do just fine forever with a little bit of maintenance and nothing more. For people that fall into this category, it will be free forever