Why don't they upgrade search filters?

They might. Each update adds new filter options. The latest one brought us the exclusion instruction in the form of "!" (no quotations), so we can now filter OUT by specifying undesirable results in the following format:

!traded (will filter out any Pokemon that have been traded to you).

You can also mix it with other search queries such as:
traded&!lucky
which will return all pokemon that you have received via trades and exclude all lucky ones from the list.

Maybe you want to see your lucky legendaries that aren't shiny so you search:

lucky&legendary&!shiny

Or all your dragons that do NOT know any dragon moves:
dragon&!@dragon

just to name a few examples

Also it would be good if we can filter normal / charge move type separately (or both) like we can do in DPS chart here (<*>grass)