Can someone tell why are we donking here ?

BB 3bets a lot of trash he also has TT-KK which are not super strong otoh SB calls pre with lot of Ax and hands that connect to the 98, so board is not that great for BB.

Despite having an equity disadvantage, SB's range is more polarised. There are very few hands with middling equity, so more of their strong hands are allowed to go ahead and bet for value.

If you gave SB more hands like 9x/TT/JJ, then there would be less donking. Now the strong hands need to check in order to help the marginal hands get to showdown.