Sadly we will never know the true answer to this. It would not be that unusual for the band to try out different songs of their first album together. Maybe they did it once or twice and never bothered again. The While Album tour was unusual. It started before the White Album release and had various legs across the U.S. In August 1975, the White Album just hit the Billboard charts at #183. 13 months later it would hit #1 in September 1976. Sugar Daddy was the flip side on the Rhiannon single 45.
I am curious why Warner Brothers did not squeeze out and promote another single. Warm Ways tanked in the UK. Over My Head did fairly well and the last 2 singles were big hits at #11. Was Sugar Daddy thought of the 4th single? Total pipe dream and not true but its fun to think of the possibilities. Maybe we got to see cheap Mick in the early days. Maybe he feared Sugar Daddy would be a hit and because Waddy played guitar on the song, the band may be forced to pay him LOL
To quote Mr. Buckingham: "OMG Fleetwood Mac with hits!"