Because the most common people complaining about Bluesky fall into 1 of 2 groups:

People upset that Bluesky isn't tolerating their behavior (mostly Nazis and transphobes angry about the community not letting it become Truth Social 2 or allowing transphobes to harass users, but also certain leftist groups, much like the tankies here on Lemmy)

People upset that the infrastructure isn't FOSS or some similar complaint about it not being enough (purity test behavior like in every comment section on Lemmy)

And people saying that Bluesky is an echo chamber tend to fall very heavily into group 1.