If the search length was allowed to increase, it would dramatically slow searches down. It would take a 'lot' longer to get search results back, and possibly the search would stop before gaining as many results as it does now due to the search stalling.

Best is to search one criteria at a time. Sleepless's music search advice principles also apply to video: How to find music

I know this is limiting, however, if you search using multiple criterias then chances are most of what search results you get back will be spam unfortunately.