You created your account with mastodon.social. My mastodon account is with techhub.social. So your eggs are in that basket, but my eggs are in a different basket and others' eggs are in yet more baskets. You can argue that all of your own eggs are in one basket, but not everybody's eggs are in that one basket.

Some narcissistic infantile billionaire could buy out mastodon.social and burn it to the ground, but the rest of the Mastodon network moves on. You'd have to relocate, which is a pain, but you're not relocating at the same time the rest of the world is relocating. Decentralization is resilient, not bulletproof.