well i had the same question, but then i realized what riot aim is...
they didnt implement a progress bar for various reasons, but the most import thing of it all is to reduce the Saltiness in the game...
think of it this way, knowing how much honor u still need to get to the next level or max the 5th level will put you on a mind track that after u get to this point u can be salty again... but, not knowing how much progress u had done and when u gonna level up, your going to keep that temper of yours controlled so your honor wont drop...
another point of it is, that with a progress bar players will abuse the system level up harvest the rewards drop back again then level up again to harvest the rewards over and over again... i kinda agree with riot on this, no progress bar has reduced saltiness in the game a BIG TIME, now players are more nice and understanding even if u feed ur lane and u tilt they tell you its okay we all have bad games and stuff, this is amazing...
Riot please do not implement a progress bar i beg you, keep it this way, let players guess and be excited to when they will get up a level, so they stay cool and calm as long as possible.[slayer-jinx-catface]