Why No Power Button on Some Phono Stages?

I am upgrading my phono stage, and several of the ones I have shortlisted do not have a power switch/on-off button.

Why is this? Is the user supposed to keep it powered up all the time, or manually unplug the power each time?

I know certain electronics are supposed to have better sound once they have reached thermal equilibrium, but that doesn't mean I want to keep it powered up 24/7.

Switching the phono stage power off from the power strip is a PIA, as it would switch all of my other components off, and I'd lose by tuner settings.

I want to choose the phono stage by sound quality, but an on/off switch is a major convenience factor for me. Why do some manufacturers leave it off?
I turn my doorbell off when I leave the house. It doesn't seem to have any effect on the sound.
"While I do agree that it's optimal to listen to components when they are at operating temperature, I would like the option of turning off a device easily when I choose to..."

Plan on several days for optimal sound with solid state devices.
Several days? That's just silly...turn off everything when you're not around, or at least never admit that you leave things on, as these days that's simply lame. Really.
A point that I don't think has been mentioned yet is that depending on the specific design leaving it on all the time might result in greater long-term reliability than turning it on and off, especially if that is done frequently, as a result of reduced thermal cycling.

I use the phono section of a vintage Mark Levinson ML-1 preamplifier as my phono stage. The ML-1 has no power switch. Although I am not its original owner I know that it has been powered up for essentially all of the past 35 years, and its phono section works as new. (Its line stage, which I do not use, did develop a problem a few years ago after being powered up for 30+ years).

However if you do want to turn off a phono stage having no power switch, without turning off power to your tuner or other components, just get a power strip (one that is just a power strip with a switch but includes no filtering or conditioning) and plug its power cord into one of the outlets on your existing strip or conditioner. This Hammond model would be a good choice, if its physical size is acceptable to you.

Some folks might assert that doing that would adversely affect sonics, but IMO any such claims would be speculative, technically unsupportable, and unlikely to be based on experience doing the same thing with the same or similar equipment.

-- Al