It’s because the drink manufacturers mostly just stopped selling the full sugar versions
Which was a result of the sugar tax. They didn’t just suddenly drop the sugar content for no reason.
The sugar tax didn’t include artificial sweeteners? That’s an oversight. Those things are bad for you in ways that are different from digestable sugars.
They’re nowhere near as bad as consuming a huge amount of sugar.
They only cause issues for a vanishingly tiny amount of people that have pre-existing genetic conditions.
That’s highly debatable. It’s swapping one set of side effects for another, especially when drunk at high volumes.