Bubbles will only be interesting as a decoy till people won't pay attention to those...
Are you implying that awareness of effective strategies would become common knowledge? In this game where brush, roller, and aerospray users will charge face first alone into enemy ink when being spawn camped instead of building special? In this game where people with charger weapons will gladly run to the center stage and try getting into gun fights like they have a shooter? In this game where people will superjump every time to someone --ANYONE, regardless of safety or distance from the spawn?
Is the Splash Wall bad because it doesn't get kills and it breaks after a single bomb throw and a few shots?
Even if they don't focus their fire on the bubbles, the bubbles still force the opponent to respond to them, either by moving for fear of them popping or them blocking their shots which is again, the point of the bubbles giving stage control. And it gives something for your other players to use. Bubbles are a huge signal to other teammates that "Hey! Something is happening over here". Say a Forge player is having a one-on-one with someone and they throw bubbles. A teammate can take advantage of them to assist the Forge player from a distance by firing at the bubbles making the enemy player run or killing them with the pop, all while the bubbles are eating the enemy shots that are aimed at the Forge.
It's just like Tenta Missiles. The missiles aren't going to get a lot of kills, are terrible panic tools, and are pretty easy to avoid if you know what you're doing, but they force the opponent to act in ways they don't want to. And that's the point. Tenta Missiles are long range stage control, bubbles are "close" range.