Or, to play devil's advocate, that you aren't putting in the level of work in your day job that you could be putting in. If I were an employer looking at a candidate and I saw they had huge amounts of open source contributions, the first thing I'd ask is "how did you have time for this and your day job?".
It also tells you something else about a candidate: that their previous job probably wasn't particularly hard or that they didn't have much in the way of responsibilities. If you're the lead developer on a several hundred thousand line codebase, it seems less likely that you have time to build an open source resume than if you were a junior developer.
Honestly, I think open source is a bit of a mixed signal. If the code shown in the repositories is great, then that's fantastic, but if it's merely average then I think it makes you look worse than just not having it there at all. This is really my biggest objection with open source: if you want to use it as some sort of resume, then you have to contribute huge amounts of time to it in order to make it representative of your skill. Then it's no longer an open source project you do for fun, but just a second day job. Additionally, when it gets good enough for an employer to see, what interviewer is going to have time to read through it? This problem is magnified especially when developers start treating open source as a form of resume, and interviewers have to wade through shockingly poor repositories from every candidate to determine the candidate's quality.
It also tells you something else about a candidate: that their previous job probably wasn't particularly hard or that they didn't have much in the way of responsibilities. If you're the lead developer on a several hundred thousand line codebase, it seems less likely that you have time to build an open source resume than if you were a junior developer.
Honestly, I think open source is a bit of a mixed signal. If the code shown in the repositories is great, then that's fantastic, but if it's merely average then I think it makes you look worse than just not having it there at all. This is really my biggest objection with open source: if you want to use it as some sort of resume, then you have to contribute huge amounts of time to it in order to make it representative of your skill. Then it's no longer an open source project you do for fun, but just a second day job. Additionally, when it gets good enough for an employer to see, what interviewer is going to have time to read through it? This problem is magnified especially when developers start treating open source as a form of resume, and interviewers have to wade through shockingly poor repositories from every candidate to determine the candidate's quality.