Strange indeed, and I have a feeling the feature was there back in 2018.
I may be wrong though.

The way I interpret the FAQ, as the median price is somewhat controlled by the witnesses, those in charge of the official frontend didn't want that feature available to everyone. I am not certain about that but it also looks like limiting the witnesses influence over the price and letting more the trades to weight on it. Probably more than one reason for removing it.
I'll have to check if other frontends still have the convert feature available.