Starting out, it helps keep cost low while still having presence in multiple platforms. I hate every electron based app I use but that's exactly what I would use in an early company.
Can't really say much about bigger companies though.
It's much easier and cheaper to find engineers that have web technology experience as opposed to those that have native mobile development experience, hence part of the draw for bigger companies. And the ability to share code is a non-negligible optimization at scale.