Also virtualization - VMWare started out as the dominant player, but then Xen came out, which first led to AWS becoming dominant but now results in a number of cloud hosting and VPS providers, many of which are more cost-effective than AWS.

And PCs - it started out as a decentralized market between Apple, Commodore, Tandy, Atari, Osborne, etc, but then centralized under IBM before being decentralized again with IBM clones like Dell, Compaq, etc. That in turn forced the centralization of the OS market under Microsoft (driving out Apple, CP/M, Acorn, Atari) and microprocessors under Intel (driving out Motorola and MOS technologies).

I think it's more accurate to say that the point of centralization moves up and down the value chain based on technological developments, market deals, and corporate strategy. When things get too centralized, a savvy entrepreneur will come in as a small-time complement, then find a way to encourage competition and commoditize his complements, riding the wave to a very prosperous monopoly. When competition becomes too intense in those markets, the bigger players will start eating the smaller players, and eventually the market consolidates.