They are pretty much a thing of the past; MLB isn’t gonna give you anything at half price anymore. I seem to recall one or two have been scheduled in recent years, I believe by teams with poor attendance, like the Rays, as something of a promotional effort, but that’s about it. A few traditional doubleheaders will happen here and there to make up for rainouts, but even makeup games are, whenever possible, played as day/night split doubleheaders so they can charge admission twice.
Teams only add doubleheaders if a game is rained out. They are never scheduled in the beginning of the season (to increase income, obviously). A day-night doubleheader (two admissions) is more common, but sometimes it’s not logistically possible.
I did go to one years ago. The thing was that we didn’t realize it was to be a double header (it was making up a rainout the previous day) and we wondered why the game seemed to have started early, and didn’t know there’d be a second game.
During the 1970s I attended about ten doubleheaders, all single-admission. Almost all involved the Cubs; the other was White Sox at home against the Twins. I went to maybe four more in the eighties, but none since 1987. By then doubleheaders were considerably less common. It;s also true that I became a father in 1986.
I definitely enjoyed the DHs, and I always felt like I was making out like a bandit by getting two games for the price of one (especially when I reached my teens, about 1974, and started going to games on my own sometimes, in which case I was responsible for paying for the ticket myself).
I don’t know that I would have the stomach for them now, though. Games are just too long and I have too many other things to do. Someone I know went to the Phillies-Mets game last Sunday and reported that the game took 4 and a half hours (9 innings, yeeks). I looked up a couple of the early doubleheaders I’d seen and found that the two games together didn’t last that long.
–Doubleheader games are just seven innings long in the minors, and I have seen the first games of several MiLB doubleheaders over the years, but never stayed for game 2. Just too much of a time commitment. Oh well.