Very good question. Add this to the list of completely bonkers decisions by the Muppets at Apple. There is no reason apart from the fact that they don't want it.
I suspect it'll make its way to the iPhone/iPad eventually. I believe this was a new feature in watchOS 8. Even the HomePods support multiple timers...and you can name them!
Workaround for now is to tell Siri to set an alarm instead of a timer. (ex. "Set oven alarm for 10 minutes", "Set cookie alarm for 15 minutes.")
Agree, and why did they take away the alarm notification on the home page?
Seriously inconvenient that you can't check that the alarm is set to go off when you are half asleep in the dark without have to make a couple of manipulations and look for a tiny clock icon that you can only see wearing glasses. (For some of us).