A couple of forumers have had some plausible reasons why a reset would not be ideal:
For me personally, the thing is, if one is of a certain skill level; no amounts of resets would make him or her better. They would still just either rise or drop to their actual skill level.
Personally, i have played against people who are over 3000SR in Arcade Mode games and i get totally destroyed. Based off my SR from last season, 1537 and starting off at 1336. Over the course of 20 games which it took me to get there, i can safely say that i was having competitive games which could have swung either way and i firmly believe that despite what my 80% win-loss ratio may imply.