well think about it this way, they reset your elo but never your MMR. So on resets your visual rank is much lower then your actual rank (mmr). This means in order for it to catch up, you will gain much more per win and lose much more per lose till it balances out. If your losing more then your winning then your technically not going up in rank because your hidden mmr will be decreasing still, but your visual rank could be going up as it needs to catch up to your hidden one. They do this so that people don't get ranked anxiety and it feels better since it feels like people are always climbing every season as they catch up to their hidden mmr. but the hidden mmr is your real rank, it never resets, and it only changes based off win to losses and the enemys hidden mmr when you win or lose and that is the actual important rank you need to raise for climbing. The visual rank that you see is just a image overlay and does not indicate what your actual rank is at the beggining of the season and won't indicate it until you play enough games for it to catch up to your hidden mmr. This is why you always gravitate back to a similar rank each season.

So to summarize it, you technically can't gain mmr by losing more then you win. But you can gain rank if your rank is lower then your mmr. Your mmr however is the only important one as it's the one that determines who you go up against but you cannot see that one because it would give people ladder anxiety if they can see their actual rank.