The simple and most accurate reason for blockchains burning their tokens is to improve the performance of their system. It can equally be referred to as the strategy of amending and upgrading a token's value.
This gave rise to a concept called "Proof-of-Burn (PoB)". Although many people believe it is similar to the proof-of-stake mechanism, as they both make use of their native tokens to secure their networks.

In fact you’ve said it all, blockchain networks burn their tokens in order to improve the performance of their networks