Please correct me if the flow is wrong, but when searching for a module, you may have a situation where the module that you are looking for exists, but it's not compatible with your current Drupal version. The outcome is that it won't even show in the search.
That is confusing, and it is hiding modules that could benefit from contributions of third party developers that, for example, need the module and even could help contributing with a small MR to fix the compatibility
It also gives the wrong picture of the modules available for a given problem.
Search for a module that is not compatible with your existing current version. Modules that exist will not appear.
All modules should appear based on the keyword. If a module is not compatible, it should be displayed accordingly, maybe using a grey background, or a red message that indicates that although the solution exists, it's not yet compatible. Maybe add as well a link to tell the maintainers to update, or instructions on how to actually help.
Closed: won't fix
1.0
User experience
We are displaying modules that have a release compatible with _this_ version of Drupal. We wanted to keep Drupal 7 ("legacy") modules out of there, and I think this is the best-case scenario. We do intend to document what shows up and what doesn't, and why, and encourage folks to use Drupal.org to find the full suite of modules.