Why do bots sometimes suck?

I was playing a match on unfair bots as Drow Ranger and I got 19/2/2 KDA

However all of my teammate bots were so bad it lost me the game. I didn't do bad and ended at level 22. However the bots on my team ended around lvl 15 and the bots on their team were 19-21. It's pretty infuriating when the bots you play with suck. You'd think that their skill increases or decreases depending on how well the player is doing.

Here's a link eexplaining the bot mechanics :P
Bots (dota wiki)

It explains what happens.

(TL;DR: Bots become less difficult on your team the more human controlled players exist in the game on your team.)

It was just me on my team with bots. Thanks!

Huh, funny how it says the teammates give a "small" advantage to the enemy team yet they gave a huge advantage >.<

->This explains me feelings on the matter<-