Fixing these defects will cost hundreds of dollars, if not more. Given the age of the parchment on which this Torah was written, ink does not get absorbed as readily as before. That means that every year we will find more and more defects, costing us hundreds if not thousands of dollars.
Please excuse the analogy, but this is very much like the economic logic of car repair. A repair may cost only a few hundred dollars, but the owner knows that even more repairs will be necessary in the future. That being so, it often makes more sense to purchase a new car - or, in our case, a new Sefer Torah.