Clemenza: [fish tank scene] “Don Corleone you once said that the day would come when Tessio and me could form our own Family”
It seems to me the above was the carrot Vito has been dangling and both Clemenza and Tessio seemingly were receptive of the said arrangement / reward

Clemenza and Tessio already had their own territories They could have continued to run their respective Families [like a Corleone!] without Michael on their backs

Michael can still draw the water from their well for muscle and they can certainly present a bill for such services
After all Michael is not a Communist!