My my, how times would change 10 years later where people actually want Brock gone....
Most people didnt wanted Brock gone,but that actually writers start doing something with character and its story pulling him out from stagnation.Hence explaining complaints which started already in Johto.
Brock was still somewhat interesting in Johto, and I even thought he was still OK in the AG days...it wasn't until DP that it became obvious Brock had lost all purpose in the series.
People and heir double standards.Misty was more interesting and active than Brock was in Johto,but for some reason that is ignored.
Speaking of Brock,its rather exaggerating to say how he lost all purpose in DP. Brock career as breeder actually received better treatment in DP than it did in AG.For start his pokemon received better focus overall(especially Croagunk and to extent Happiny).He got for first time pokemon egg raising it to healthy Chansey which allowed that h use breeding skills to full potential.His character got some pretty good focus and interacting between some characters(like nurse JOys,Holly,maid girl from MIltank Cafe)and he did had some mmorable moments with Ash and Dawn.He also got to play some role in Team Galactic arc,won pokemon transformation contest,participated in tag battle tournament etc.
Main problem in Sinnoh was that focus was often put on Ash and Dawn being two co-stars around who story revolved with Brock character often being left behind not being given much attention as character.That and emphasize on Ash and Dawn friendship forced Brock out of group dynamic.
Somone may say,but Brock wasnt getting much in Johto or AG either.Well compared to DP it was significantly more.
Its needed to remember how Dawn received much more focus than Misty and May did being almost equal to Ash with there no being left much space to give more to Brock.Majority of DP episodes were about training of two co.-stars pokemon,practicing for appeals,focusing on their rivals and contests and gyms respectively.Likewise passiveness of his breeder goal also represented issue since this didnt had much to do with battling ,competing or having benchmarks through which progression can be measured .It was mostly about taking care of pokemon,preparing food and keeping them in good form representing problems for writers to give him more to do.
When formula changed afterwards with BW this allowed writers to better distribute focus among main cast.Cilan wouldnt get half as much he does now if he was brought in Sinnoh instead of Brock.
Apparently the writers realized the same thing, which is why he's been finally removed.
That has nothing to do with Brock departure.People complained about Brock ever since Johto but he was still kept.Main and in reality only logical reason why Brock left after so long is because of revamp which happened in Black and White games.New generation promotes vibe of "new start"portraying Unova as foreign and isolated country with writers just mirroring games with new series.
For that reason,contests were removed after 8 years,Brock left,formula changed back to Ash as only main star with Cilan and Iris being sidekicks along with references to past being kept to minimum.
This also explains why there are no older pokemon present in Unova.