Well many of us have given this thought. Issue is it's nearly impossible to do or sustain. All it takes is a single spore given the right conditions. But how it gets there could be from the water source, your fish you introduce, plants you introduce...
People already dip their plants in stuff hoping to kill off unwanted pests and algae's. But what about your fish? Cant exactly sterilize them fully, which would stress or even kill them if you tried. Even if you dipped them they have algae in their gut that they ate... even if a single bit of it lives it will reproduce after.
Also youd need beneficial bacteria, even if you buy some from a store (I firmly believe they dont work) there is no way to make sure there isnt spores hiding in that.
The crazy thing is, most our tanks have many many strains of algae's that linger. I didnt think I had blackbeard in my tank ever. Years went by with no additional plants or fish. Then one day the right conditions let black beard take over till I corrected it.
Honestly, most aquarium tests suck. Algae sometimes can tell you things that you would otherwise miss. Such as green spot algae, if you see it then you know "oh my phosphates bottomed out"
Yeah plants show deficiencies that help identify issues but algae does too, some just let a issue get out of hand then blame the algae for it even when it's their fault for letting something go out of wack even if they arent aware.
Recently I was trying to get some of my RODI mixed with ferts to stop molding after a month or so. So I made my solution and put it into glass bottle and put it in boiling water until the inside boiled. Surely mold spores cannot survive 200+ degrees, but it still molded. The bottles had one way valves on them for autodosers, nothing could have gotten inside. Same logic applies to things like hand sanitizer not killing that last .01 percent of germs. It just take one cell that lives somehow and it gets through.
I honestly think it would be 10 times harder to have a sterilized aquarium with only beneficial bacteria than it is to do a normal planted tank with balanced conditions.
Heck most fish food has algae in it as a food source....