Wellp, there are a few reasons, and I don’t want everyone to dogpile on me for saying so. 
First, people who buy high-end lights aren’t paying for candle- or party- or lightning mode. They want a high quality reliable light, that’s easy to use even if limited. Simple trumps complex. If you’re a cop buying a Suefire or a homeowner buying a Nitecore, you want a light that Just Works. You don’t want to grab a light and have to screw around trying to figure out what mode you’re in, or worse, be checking out a noise downstairs and end up in some unknown mode. If you get stuck in manual memory or thermal config or who knows what, because you didn’t tap out the proper Morse code to turn on the light, it’s useless.
People don’t want ¼ drills; they want ¼ holes. Hence, they want a light that’s predictable in a pinch or emergency situation.
One of my fave lights, the Acebeam EC50, has as simple and useful a UI as you’ll get. Click on/off. Press’n’hold for moonlight. 2click for turbo, press’n’hold from on to bump through the modes. Done. Not even a single stoopit blinky to be found. Memorise those 3 ops, and you mastered it.
My Anekin UC20 in PC-green is a 1-mode light, on/off only. My UC20 in white with 12 modegroups (like bis-whatever) I set similarly to 100-only. That’s all I really need. My old (still got, works beautifully) ’502 was/is a 1-mode light that did 95 of what I needed a light for, and I EDCed that for a long time.
Then again there are different switch configurations. My Nitecore MH20s/-GTs have a 2stage switch like a DSLR. Press’n’hold halfway for moonlight, all the way for turbo, otherwise click on/off. Half-press once on to switch modes. Here’s your diploma, you just graduated MH20 school.
Nitecore TM03? Dual tailswitch, both momentary-on from off, power for last-used mode, mode-select for turbo. Else click full for on/off, modesel to switch modes. Done.
Sofirn TF84, similar to the TM-series with dual-tailswitch.
GTmini, ’micro, Q8, all use narsim, nice ramping with shortcuts to moon/turbo, plus temp config and some other settings. Intuitive right out of the box, if you know basic shortcuts.
One huge complaint I have about andy is the convoluted UI, press vs press’n’hold, press from on vs press from off, etc., how they do sometimes drastically different things. You try to get into blinkies and end up locking yourself into manual memory and have no idea why it doesn’t remember that you kept it on moonlight for a few minutes, turned it off, and are now blinded at midnight because it “remembered” 90% brightness. There’s no distinction between normal/common operations and locking in settings.
Someone (Funtastic?) refuses to sell lights with andy because people who buy his lights just flat-out hate it.
And finally, people who buy high-end lights (think PD, FD, S&R, etc.) are NOT necessarily “enthusiasts”. They want high-reliability, ruggedness, etc., but do not want an overloaded UI with modes they’ll never use and which can very likely get in the way, possibly at the worst possible time.
Too many people conflate the two groups, thinking everyone who buys an Acebeam/Nitecore/Suefire/etc. must must must have andy as the underlying UI, and that’s more often than not, not the case. They want a tool, not a toy.
That said, I have an assload of lights which have andy as the UI, and I like them, but I keep coming back to lights which don’t. Nothing against andy, just that a simple UI is so much easier to use and more predictable.
