It is unfortunate that it is the case, but weather seals are typically the first thing to go with your garage door. They perform a vital function with your garage, by ensuring that moisture will be excluded from your property and helping to insulate the garage as well, but as they are usually partly made from rubber, they will eventually begin to break down.
Replacing your weather seal is relatively easy, and could go a long ways towards maintaining the health of the garage door. With most doors, you will find it easy to replace it by yourself, without the aid of a specialist, but if you don’t want to take the time to do it yourself, finding a professional willing to take the job on should be easy enough.
Replacing it is done by sliding the previous seal out, which shouldn’t involve too much tinkering, and then sliding the new one in in the same way.