So that's a valid point actually (and probably still valid today), however the more obvious reason is that 25 years there was no evidence drones had any real material capability - especially given at that time, the US had no idea they'd be involved in long, low-grade engagements.
And of course, the internet upon which our drones depend, didn't even exist as we know it now.
Drones were 'new tech' and not until they started being used, particularly in Afghanistan and Iraq 2, did it start to become very obvious how valuable they were especially in those kinds of conflicts.
Nobody predicted how incredibly 'useful' they would be.
Put all those pieces together, and you see that drones are what they are today.
And doubling down: completely useless in a conventional situation without support, cover, protection and basically superiority. A squadron of 5th gen. fighters with their great radar and support will take out any number of drones over time. As would ground based systems. With impunity. Predator style will never even come close to being 'in range' of the F35's let alone be able to target them with anything.
Drones light up on the dumbest, easiest radar, they fly relatively slowly, they have no defensive capabilities.
It's like comparing Apaches to trucks with a 50-cal + maybe a guy inside with a crappy shoulder mounted MANPAD out in the desert, with nowhere to hide.
All this talk of 'drones vs. F35s' literally when a drone has never even shot down another aircraft. We literally, just in 2018 were able to test fire some A2A munitions. We know fighters can easily clear out drones ... but the inverse is still purely speculative.
As for F35s: they are the only choice, their deployment is inevitable because there's nothing else on the horizon for a very long time. The development timeframe of new gear is growing quite a lot, surely due to bloat, but also to to complexity - an F35 is not an 'aircraft with a few missiles' - it's a 'weapons platform that happens to fly'.
A long time ago, I visited a distant family member's home in Texas, and his uncle was a senior leader on the F22 project, they were doing trials, it was very exciting! But took another 15 years (!) for that thing to reach maturity.
Surely the Americans have some things up their sleeves we don't know about, but how well deployed and useful can something be if it's a total secret? The old F117 Nighthawk was kept quiet until Iraq 1, but that was before the internet.
We're going to see F35s and upgraded 4th Gen Fighters in the mix for a long time. Canada is using it's F18's something like 3x longer than planned.