There is no franchise tag but there is a salary cap. Trying to fit 3 max/near max contracts under the cap via free agency while trying to fill out a roster is not easy.
Stars didn't do it previously because they didn't have to. They either walked into a star studded squad or their FO put stars around them. It's not like stars have never played together before. Are you familiar with NBA history?

at you mentioning KD. He's the perfect example of a star playing with other stars. Why would he leave Westbrook, Harden, and Ibaka?

Some nikkas walk into good situations, some nikkas wait around for someone to improve their situation, and others improve their shyt themselves. In every context but sports the latter is praised as a go-getter and ambitious and having a take charge attitude. Did you watch the playoffs last year? Was that really an easy ring?