There are many reasons why one would choose to re - sole a pair of welted shoes.
Instead of just buying blake stitched shoes and topying them again and again. Or buying cemented shoes and topying them again and again.
While not a hard and fast rule, the better constructed shoes are also typically made with better materials. And the lower construction methods are also typically made with poorer materials. For example, you will hardly see cemented shoes made with first cut full grain leather uppers, and you will also not see Japanese bespoke makers making a pair of bespoke shoes with corrected grain leather. GYW shoes may fall somewhere in between.
As such, a pair of welted shoes made to the best of standards are also usually made with materials meant to last. A resole can also bring a good number more years to a pair of shoes whose uppers have already moulded to your feet, and which you've spent time conditioning, polishing, building up a special character on, for a few years. A pair of shoes can go beyond just dollars and cents.
Moreover, though this might not be the preference for some, the welt and the outsole on welted shoes actually acts as a protective "barrier" as it protrudes some distance from the uppers. So when your foot kicks against something, the uppers are less likely to get damaged. Then again, if someone is buying shoes with a topy and throw away mentality, then it probably doesn't matter.