Getting a new baseball glove can be expensive. This is probably one of the two biggest reasons to repair your glove. Relacing, cleaning and conditioning is cheap compared to buying a new glove and it is not that hard to fix and clean up your glove.
Breaking in a new baseball glove can take some time and you may not have that time right in the middle of the season. New, expensive gloves with the "real" leather can take a whole off-season to break in.
Your baseball glove is custom-fit for your hand, you play well with it and you just don't want to give it up for a new, stiff glove that you'll have to break in.