Isn't the volume of Wasabi coinjoins infinity?

Coinjoin [and similar protocols] have finite throughput, limited by available liquidity; it can be increased by services like Joinmarket, although you can convince yourself of an upper bound by realizing that if you require having at least N counterparties, then your largest coinjoin size is 1/Nth of hot UTXOs... in practice most are not interested in participation.

Naive repeated use of the same fungibility pool has diminishing returns in terms of improved pseudonymity per fee paid, and might even become counterproductive if producing an overall transaction graph where entry and exit are obvious.

tl;dr the most important ingredient of privacy is patience.