The point of a bowell cleanse is likely not single faceted, for one reason because the point [s] is dependent on the individual - why did somebody do a bowell cleanse and was it done with short term expectations or long? There is also bio-diversity in play IE. we are all humans similarly designed but_not_identical in our internal bodily processes. Thirdly, the many bowell cleanse methods out there are not one and the same but some are similar. I may be mistaken but recall Hulda's was based on the larger program of dental cleanup IE. she advised that for the best results, have all mercury fillings removed prior to doing her cleanses (3) for kidneys, bowells and liver.
In the short term, one bowell cleanse, or even a couple, primarily serves to purge, as you said, or in other words, to unclog some of the gunk in the lower digestive tract, what some call lower bowels and others call colon. 'One proof does not make a puddin', a bowell purge done once or a couple times will not make a person " more regular" in the long term but may lead you to believe the purge caused subsequent constipation. You just finished purging your lower "sewer" system of contents thst were partly helping you to experience whatever was your "regularity" prior to the cleanse. The cause is not the bowell cleanse. The cause long term is the cumulative effects upon the bowells after years of diet/lifestyle/genetics (DLG) and no matter how any one person has / holds or has been dealt these three cards, it is unlikely this long term condition is going to be significantly improved after a couple 1, 3 or so cleanses, nor after a month's worth nor after a year's worth of regular cleansing.
Regularity is somewhat of a misnomer, for some people it may be once a week, for others it may be two or three times a week, neither of which are really all that regular but this is how different people have different interpretations of the same word. Two or three times a day every day is specimen regularity. For me regularity is usually once a day every day, on occasion I go twice a day and if I go a day or two without I am either coming down with an illness or have been REALLY over indulging the DL components of DLG. I often eat 1 meal a day and have observed that often ..... regularly the bm happens shortly after the meal ..... I think of this as basic plumbing and pressure at work. Putting a bunch of stuff ..... food .... mass...into the top of this plumbing system adds pressure ..... force .... to whatever is already in some stage of passing through the lower parts of this system, the pipes that ingress at the head and egress at the rectum.
Ive used various bowell cleanse methods including Hulda's , Schulzes as well as coffee enemas and while all three generally produce the same visible results, from experience I know that there will be a two to three day lapse between the flush and next BM. Schulze's is a more comprehensive approach but I prefer CEs when I need or want to purge the low bowell quickly with the added benefits of flushing the liver ( and bile ducts) thanks to the coffee solution cleansing the blood via the Hepatic vein located at the high end of low bowel and if the enema solution goes high /far enough it may also help flush the Appendix.
I can relate to your agitation .... sentiments. The first time I ever tried any bowell cleanse about 12 years ago, I went to health food store, found the shelf that had .... 10 to 15 separate brands , i stared at the shelf a good ten minutes, eventually grabbed the brand that had a graphic on the bottle depicting the colon, went home and began taking the capsules daily with the naive belief that by the end of the bottle I would have corrected 40 plus years of DLG ..... boy was i disappointed upon being disabused of this notion. Doing things to help improve bowell function becomes an endeavor that will last either the rest of your life or to the point you decide it is not worth the effort. Good luck!