In order of significance:

• Way smaller scale

This is the most significant part, large scale means entirely different problems to tackle.

• Less functionality

Seen from the perspective of the codebase. Some of this functionality is not of interest to the users (tracking etc). All code executed takes time in some way, shape or form.

• Younger codebase

Lemmy has had less time to accumulate cruft compared to reddit.

• Written in Rust vs Written in Python

Not super-significant at the end of the day, but it does make a difference.

Well its not loading any bloat for one. No ads, no trackers etc. Also its less that a fraction of a percent the amount of data on what is actually decent amount of processing power if some of the instance specs are accurate.

For one, open source solutions tend to be better coded, as there is more passion and less underpaid IT under heavy pressure to release asap.

For seconds, there are many servers, so it's less reliant on one systems performance.

And third, but not least important. Way less users, meaning way less bandwidth usage. Time will tell if speed stays the same when the amount of users increases significantly.

Because its Rust