They were shockingly unreliable and incredibly expensive. Tubes have a very low mean time between failure, so any design that uses tubes exclusively can't work for more than short periods without breaking down - possibly minutes, maybe hours, probably not days, and absolutely not months or years.

And each failure means a cycle of fault finding, which can take hours or days in turn.

As a technology it sort of works in a prototype way - you can get some work done until you can't. But the unreliability means it's qualitatively different to a modern laptop or server farm.

The wonderful thing about integration on silicon is that it's the opposite - it's incredibly reliable, as long as you keep the thermals reasonable.