Janie, Your suggestion would absolutely make searching a lot easier, but - and it's a VERY big "but", I'm afraid ...
There are also many other options that would also be very helpful to have available in the search function. Unfortunately, any additional complications added to the search operation would require very significant changes to the software that represent a major development effort and WikiTree just doesn't have the luxury of available software development time. In addition, there would be a negative aspect to adding any complexity to the search process - that is the additional processing time to produce the resulting list. Depending on the degree of complexity, it might even impact WikiTree's response time to all requests while the search is processing, not just the single search request.
Bottom line - I agree that the search feature here leaves a whole lot to be desired, but I understand that the price (in both development effort and resource usage) is probably way too high for it to ever be considered.