Hmm, I think you are overlooking some opportunities for marketing here.
Just one example: If your product solves problems for users of another type of software, that the makers of the other software don't want to take on, they can be a source of referrals to your shop. One example might be a password manager referring people to antivirus / antimalware.
Often that physical placement of the storefront has planning behind it, too.
@JMMaok One example might be a password manager referring people to antivirus / antimalware.
Ooh that's a good example of cross promotion, have you come across it?
I feel like I probably have, at least in terms of newsletter-style emails, or maybe breach notifications? But no, I don't have an example handy.
Another example that comes to mind is Taiga and PenPot. Different products by the same company https://blog.kaleidos.net/Taiga-and-Penpot-lead-our-new-chapter-at-Kaleidos/ In my experience they do less cross-promotion than they probably could. I am just a dabbler in using both products. They may do more cross-promo than I've seen, or have good reasons for not doing more.