"If anyone in the top 5 of the ladder got banned then you were see a very significant effect to peoples ratings."
Yes, but you are right for another resone then what you are arguing. Lets presuming that A and B never left the ladder, gets suspended and looses games forever. Their rating would rather quickly be the two lowest in the system. A boot win against either of them don't have to much impact. (For example removing my 4 first wins only gives me 4 more rating points) So since Bayeselo always recalculate the rating, the boot wins will have the same or very similar impact after some time. However, the real issue is that top tier player will have some unexpired wins and it is the beaten players who lost to A that will really suffer. In an extreme case, the A player who has beaten, say me, becomes the lowest ranked player.
Since I played with Bayeselo, lets assume I lost to Mister Kl @ 746 rating.
Before/Now I have 2172, after the loss I would have 2134.
Though in reality the impact will never be that big. Inactive players are removed after a while, (14 days, https://www.warlight.net/Forum/105924-suggestion-autoremove-players-booted
) So the max impact is maybe 15 points. (Since you had lost to the player in the first place too.) Basically even in a worst case the rating impact is not that huge. It may be significant, nevertheless.
Anyway, back on topic. Not removing suspended players is simply just stupid.