This is a consequence of computers + internet. 2 ways in particular:

1. Large organisations become unwieldy - computers help track and tame that complexity.

2. Geographically distributed organisations have trouble communicating and can be outcompeted in a region by a company focussing on that region. The internet helps reduce the friction in communication.

Once both of these started getting adopted in the 90s and 00s, big companies became more competitive relative to smaller ones.