They are partly funded by people's taxes. Commercials have more restrictions on them than on non-public channels. A maximum of 10% of airtime can be a commercial (on a yearly basis), with a 15% max per day. Commercials can only be before or after a program, not within. And just like commercial channels, you cannot sponsor news programs.

https://www.rijksoverheid.nl/onderwerpen/media-en-publieke-o...