Indexable pages with less than three incoming links are reported by us because we consider indexable pages important.
If you want your pages to be indexable, you also want them to rank and visitors to find the information they are looking for.
For this reason many links from other sites should refer to these pages. Strongly linked pages are thus more often found by users and have a higher OPR.
If you want to check the incoming links of a page, just click on the small magnifying glass next to the link. This will redirect you to the URL Inspector.