why do I have to keep rebooting my wifi

I sympathize.  The Sonos system is indeed not reliable

My experience is slightly different from yours. The system works well for a while. Weeks, months. And then it stops working. Speakers disappear, music stutters, etc. The Sonos hello desk lets you jump through the same hoops every time but the ONLY thing that works is to reboot everything. Unplug all speakers. Reboot router. And if that doesn't help, hard reset the speakers. 

And no, it is not a faulty router. I've had Fritz, Asus, Netgear, Amplifi, Unifi. Surely Theo are not ALL faulty. 

This all would be acceptable if Sonos had a remote reboot possibility, like a batch file that would reboot all it's equipment. Then all I'd need to do is run the batch an reboot the router manually. And wait ten minutes.

My Sonos speakers are the only network devices that require regular router reboots. All my other equipment works just fine.

Bottom line, after all these years, the system still is not reliable.

Final word: I have two systems. One is a small system of three  speakers; that works without trouble. The trouble occurs in my system at home that consists of about 20 units. And setting up a large system over and over again takes a lot of time. 

I have installed and reset it many times, but some speakers just stop working after a while. The app shows that there is a connection and that the box is playing music, but you can’t hear anything. It’s very frustrating. I have two systems (one in my camper and one at home), and both are unusable. It’s terrible!

Have you set reserved IP addresses for each Sonos device in your router settings? This usually helps in scenarios such as yours. Not always, but worth the small effort. 
 

Get a better router.