Is there a reason why botlane has to be underleveled?

I mean is there a real balancing reason behind it since RIot can just slap a "+XP gain for you and your ally" similar to morde W on any support item to make the botlane have equal levels.

People almost never talk about this when talking about botlaners agency but the xp difference does really affect the gameplay a lot especially since most games are decided at 20 minute mark by gaining/losing the control of objectives, solo laner doing well will be 2-3 levels ahead of both support and adc, this doesn't only translate into more damage cause of higher ability ranks but more of everything.

Looking at Zed, a standard mid laner, if he farmed well and got 2-3 kills he might very well be 3 levels ahead, this translates to 255 more hp 10 more damage, 10 more armor and 5 more mr roughly than you or your support, this is just considering that you have similar stat growth.

So is there really a reason for this, was this something that's an intended feature or just something that no one thought to be important cause (not)having more than a 1000 gold of stats at mid game where most games will be decided isn't really balanced in my opinion.

And no this isnt me calling for ADC buffs, this affects you whether you're playing botlane or not, how many times you get frustrated by your bot being free food and useless just cause they've fallen behind and now there isn't only a gold difference but an xp difference as well that might be just as important.

Honestly i think the game would be less snowbally if bot had the opportunity to gain levels at equal pace as the rest of the team, it would help them survive 4 man dives, it would help them fight around dragon pit and it would help in team fights, since recently all i see is one fed player whatever role he is, carrying the rest of the team almost alone, just stop for a minute and think how many games have been decided by one that looks at your botlane and thinks hey free kills and kills them over and over until they can one shot everyone else