Here’s one reason, in Dr Ambedkar’s own words:

Humanity does not only want economic values, it also wants spiritual values to be retained. Permanent Dictatorship has paid no attention to spiritual values and does not seem to intend to.

The Communist Philosophy seems to be equally wrong for the aim of their philosophy seems to be fatten pigs (without spiritual values) as though men are no better than pigs.

Man must grow materially as well as spiritually.

[Ref: BAWAS, vol 3, buddha or karl marks, page no. 461-462]

(Words in brackets are not part of quote)