SQLite was late to the party. The first code for SQLite was laid down in 2000, years after MySQL was already well-established in the LAMP stack.

Also, SQLite is embedded, not client/server. That means that the application needs to run on the same machine that holds the data. And because there is no server to coordinate access, concurrency is necessarily limited.

On the other hand, SQLite arrived just in time to get picked by smart phones, and is consequently the most-deployed database software in the world. There are far more instances of SQLite running today than there are MySQL instances.

It doesn't allow multiple concurrent writers easily - you have to handle the "SQLITE_BUSY" errors yourself and cope with any changes that might have happened in the interim (although transactions can obviously help.)

https://www.sqlite.org/lockingv3.html