I'm not a DBA, and it could very well be that it's because I'm coming from the LAMP world, but when I need something light and simple, MySQL or MariaDB fit the bill a lot more than Postgres.
In MySQL there are five steps: Install MySQL (creating root user at the same time), CREATE DATABASE X, USE DATABASE X, CREATE table Y, work.
If I need something more secure, I'll add a "Create User"/add permissions step in there.
For some reason, step 2-4 (create user and set up database/table) give me a headache in Postgres.
Googled that and not one result on the first page mentioned PostgreSQL. I don't think this approach is a common one at all. More to the point, I'm not sure i've ever seen that set of instructions anywhere, ever, for pgsql. Every tutorial and intro focuses on running 'createuser'.
Oh, yeah, and you'll need to be root to go in and futz with your pg_hba.conf file, then have permissions to write it out and restart the server (probably as root).
This 'createuser' approach hasn't been a '5 minute experience' - it's been the approach that is promoted as the default answer/approach almost everywhere I've ever looked for several years.
Sounds like Postgres could use some initiative to make the experience easier/faster for beginners and new deployments (if popularity is something valuable for them). That's what many people value in MySQL apart from the familiarity.
I rarely come across tutorials for beginners where MySQL isn't treated like the only option, even if only by omission. I wouldn't be surprised if students only found out about the viability of different databases after a few years.
Biggest difference for me is that MySQL always pushed a simpler user structure while most *nix Postgres packages prefer having corresponding native OS users by default (PAM vs password auth). Also, it always seemed easier to migrate/upgrade MySQL data folders compared to Postgres ones. The specifics aren’t coming to mind right now, though. Finally I know way too many folks who prefer phpMyAdmin, especially when provided from their cheap shared hosting provider.
Don’t get me wrong, I prefer Postgres generally too, but I can definitely see wins to MySQL on ease-of-use. Especially the less standard but more forgiving SQL syntax and simple DESCRIBE commands. Yes the quirks add up for MySQL but Postgres has its share of quirks too.
