6am in my time zone is two different times in UTC. Right now it is 14:00 UTC. But when DST starts it will be 13:00. So what UTC value do you insert into your database for the opening time of the coffee shop? And how do you convert?

Yes, you can store additional information to decipher the meaning of a UTC time but why? Storing locale is good because sometimes you need to know where something is, such as when converting the local time to another zone. But you should avoid creating dependencies between these values because it makes using them individually harder.

The coffee shop opens at 6am. That is an unambiguous fact. The coffee shop is in Seattle, WA. That is another unambiguous fact.

If the time is in UTC then you need to know the date the time was set or store a dtc flag and then build some logic to convert. You can just feed local time+locale into any datetime library and get whatever you need.

UTC is great for a lot of things. Such as recording when something happened. But local time has a place as well.