Happens at least 50% of games, there's at least one person who feels the need to ping the turret that I just got the minion wave up to after pushing the lane for the past minute. As if all I was doing was going for farm.
Sometimes its good to let your team know what you want to do so they can save time by pinging to let you know they don't want to or not doing anything to show they can't be depended on or something.
Judging by your question you probably fit in the latter somehow
Because they've played hundreds of games where randoms miss glaringly obvious shit and can't stand to see it happen again.
Personally, I use the target ping to tell my teammates I'm going in on that target... right now.
As mentioned above, when playing ranked on my other account with friends I ping that stuff because that account is in low ELO and people down there really may push that lane hard not see the team fight in bot and recall because they fear the enemy jungler (who was in bot). It could also be to let the rest of the team know that someone is pushing for that objective, so do not pick a fight we cannot win, or be ready to reinforce you should you be getting jumped by their jungler. Or maybe to get the team to look that way and get in position to get a pick as the enemy heads towards you.
So, lots of reasons, though they can vary dramatically based on some information.
Oh another one could be that they need to keep the enemy from backing to allow you more time to get that objective, or to use the distraction you are creating to hit Dragon or Baron.
Pushing the wave up to turret is also a good pre-back strategy, so trying to indicate what the pinging person thinks is the right move (whittle the turret versus back) is a thing. There's also cases where sometimes the enemy laner(s) show up elsewhere, so the ping can also be a "Don't follow your laner and just take the turret as a trade" type ping, as frequently people do a little big of damage and then realize theres a 4v5 or 3v5 teamfight happening, then run to try to join it much too late instead of at least getting the objective.
Besides those scenarios, theres also the issue that everyone in low elo is low elo because they make they make mistakes that are obvious to those in higher elo, it's just what counts as 'obvious' varies a lot. I might also suggest 'obvious' things in low elo can sometimes be 'obvious' in high elo, but with the opposite conclusion, so unless you're actually challenger you might want to be wary that the 'obvious' right choice may not actually be the right choice in the big picture.
The thing about low elo and what i am seeing is, they are going to do w/e they want anyways. You can ping MIA but any other ping is near useless. Better off picking champs that do not need their team as much and playing like you are going to assume that your team will do dumb things/feed. This accomplishes 2 things. One you wont get as angry because you saw it coming. Two you will be better prepared and can possibly stop/reduce the feed. For example if you are jungler in low elo you pretty much cannot pick a farm jungler and go with the assumption if mid top bot all feed which lane would have the biggest impact in regards to what our team comp can and cannot handle and which lane on your side can carry easily if fed and doesn't take a lot of skill. For instance, it doesn't make much sense to gank for mid lane zed in low elo over your bot lane(you can but dont prioritize it because chances are even if you get him fed he is still a low elo zed).
