1. It is quite harmful to one's privacy
This is the only reason I know why address Reuse is not a good idea
2. It can leave one open to niche attacks and one becomes vulnerable to these cyber thieves who will extract private keys from signatures after a transaction has been made.
Can you tell us how this is done?
3. Quantum computers could extract private keys if these addresses are re used.
Citing an instance of the Ronin network incidence in March, where $540m worth of cryptocurrency was carted away by thieves hopefully by finding a collision of randomly picked message digest of 2¹³⁰+1 input of hashes causing possible collides by examining the square root of the number of possible output. Making re-use of Bitcoin addresses risky considering the chances of possible collisions even though the entire process might be time consuming hackers might choose to patiently wait till a collision is found just like the case of Ronin network..
Or maybe Ronin network just messed up and gave away their private keys to the hackers otherwise if this was possible, Don't you think so many addresses holding large amounts of Bitcoin would have been hacked by now?