They're your comments and I understand the sentiment, but I do wish people didn't delete their Reddit comments. Preserving what's there will help people who look in the future - we just don't have to add to it, and can (and should) devote our energies elsewhere.
Preserving but just adding a line after every comment directing people to Lemmy or wherever the user went would be much better.
The built up history gives Reddit momentum, but it's not like when you Google a solution to some tech issue and find a Reddit post from 2017 that solves it, that's materially contributing to Spez's IPO-chasing metrics. No, that's all about engagement, and active current users.
When you delete your history, you're just reducing the total information available to random people who are looking for it. It may feel good lighting it on fire but that's about it.
If we stop using it, it's just a historical record. Stopping using it is enough.