You say multi chip, but what are the signals going between chips?

Imagine all the peripherals baked into your uc were separate DIPs, and you had to worry about high speed signals going everywhere.

And yeah, all the parts were less robust and hadn’t evolved to be tolerant of less than perfect conditions.

You're right, the chips are not speaking 16MHz to each other. I've always revered the computing era where the electrical engineering actually mattered. Cheers.