1. Electricity cost
2. Need for constant electricity
3. Internet cost
4. Need for constant Internet access
5. Cost of hardware
6. Heat generated by the running hardware
7. Noise generated by the running hardware
8. Space occupied by the hardware
9. Need to update and maintain hardware/software
10. Worse discoverability for your repos
11. ISP asking questions
12. Government asking questions
13. Police asking questions
Then again, I live in a "developing" country so most of these might not be an issue for you.
A lot of these would be problems anywhere. Reliability/uptime of electricity/internet is problematic everywhere, although noise/heat I don't see why it would really be much of a problem anywhere.
Not everyone will need to self-host, it is still possible to host your projects at someone else's instance. If you live in a place where $1 is a lot of money (where is this by the way?) you could either share a server with others who each chip in their $0.10 or just find an open instance somewhere. There are plenty of organisations which host services like these, Github is the best-known but by no means the only alternative.
Gitlab, no. Gogs [1] or Gitea [2], no problem. I run Gitea on an Intel SS4200 (2.4 GHz Pentium E2200, 2 GB, 8 TB JBOD), it hardly causes a blip on this rather anaemic system. The process generally takes up around 35 MB (RSS), it talks to a PostgreSQL database server on the same box. You would not want to run a service the size of Github on this but for a personal repository it is more than enough. If your projects get so popular that they outgrow the hardware or VPS just move to a higher tier.
If you self-host you will probably never get outside contributions. For most people it isn't worth taking the time to figure out whatever system you use. I'd like to see a federated system like GNUsocial/Mastodon for git. I've thought about trying to make such a system but I don't know much about federation.
I'm not sure what exactly you're reacting to, but a lot of us absolutely do not want to self-host our github repos. Because it's work, because we don't need it, because we like using github/gitlab/other as a "marketplace"
Then again, I live in a "developing" country so most of these might not be an issue for you.