Zero offset seatposts are a waste of nice aluminum. Zero offset posts were popularized when folks started to CNC machine seatposts in the 1990’s, when machining bike parts was all the rage. Machining a seatpost with offset is harder to do, and it makes it heavier. The whole thing in the 90’s was low weight CNC’d stuff, so obviously heavier was bad. Can’t forget that more time on the CNC mill means less profitability. Those are the main reasons why there are so many of them. It’s too bad because they kinda look cool.
What’s the percent of the population that needs them? I’d say 5% is highly generous. Regardless, these posts are often found on mountain, gravel, road, etc. bikes. And they’re put there for two reasons: to control reach by putting your saddle closer to your bars, and to keep costs down.
Unless you have a really slack seat angle (around 71 degrees, Hey! Isn't that the seattube angle of a Tanglefoot Moonshiner?) or really short femurs you want an offset post. Right now so few bikes have an angle that slack and there is no reason to run a zero offset post. None. It puts more strain on knees, hands and arms because it shifts your weight forward. For long distance comfortable riding: push your saddle back. Get a 20-25mm setback post. Don’t let a sales guy jam your saddle forward and tell you, voila, the bike fits! Pro tour riders all ride 20-30mm of setback. That number has been standard for 70 years for a good reason. Setback posts allow for your fit to be both powerful and comfortable.