I don't know exactly why the devs deemed it necessary, either; however, for whatever reason, they decided to eliminate the the skill leveling loophole for the Unlock spell, and I would say it is likely they have sought to eliminate a few more of these, given their attitude toward repetitive leveling activities and the changes with Destruction magic leveling, for example, from Morrowind to Oblivion.
As for your question regarding why some of us are pleased that the devs are making an effort in this area, the answer is relatively simple.
Many of us who love RPGs derive a great deal of enjoyment from the character progression and leveling aspects of the game, in particular from carefully planning a build, weighing all the various choices, and helping that character to progress to be as powerful as possible within the parameters of the game.
If leveling Blade means fighting monsters with a sword, and you want to level Blade, such a player will enjoy not only the sense of fulfillment from progressing to Journeyman or Expert in Blade, but also, since fighting monsters is fun, that aspect will be more enjoyable as well.
If leveling Alteration means casting Unlock 100s of times on a door, and you want to level Alteration in Oblivion, such a player will enjoy the sense of fulfillment from progressing, but he or she will most likely not enjoy sitting around casting Unlock on a door repeatedly, at least it is not as enjoyable as, say, leveling Destruction by casting a fireball on an enemy, or leveling Blade by fighting an enemy with a sword.