They're likely viewing them as similar to certifications. Different industries treat certifications differently.
Enterprise technologies like Java and .NET and IBM products are helpful if you are aiming for that sort of job.
But, if you are looking at more open-source oriented shop, they give the impression that you are focusing on trying to look accomplished. It can look like you are trying to appeal to the wrong crowd, which means your priorities don't align with what they are looking for.
Make stuff. Get patches submitted to relevant open source projects. Make a small project that's actually finished (bonus if it's demo-able).
Several hiring managers have told me this.
The last time I was asked to screen and interview candidates I took the time to check out all portfolios, including github/gitlab/sourceforge profiles and projects.
In a few cases the candidate's portfolio work was decisive to greenlight and reject job apllicants.
Getting interviews isn't the hard part. Getting through them is.