Not sure of all the historical context, but remember women were not expected to be athletes, but were expected to be pretty and graceful at all times. The horses that they rode were bred and trained to meet this expectation, a good ladies hack, pretty light, and a nice mover is/was a great prize.
Ladies, of the 'upstairs' class would come out, be boosted into their side saddle, ride, then be helped off, they had no need to do anything with tacking up or horse care, in some cases the groom would have already ridden the 'tickle' out of dobbins feet for several hours before 'madam' got to ride at all.
Of course there were also great horse women, who could and would hunt, etc, and again in the right social class, without the boring need to actually work for a living, a lady could ride every day if she wished.
“Never attribute to malice that which can be attributed to stupidity”