this is actually not true.
this is usually true, but there are situations...especially top lane where diving the enemy laner is the correct call.
dyrus talks about it in one of his videos. on stream he mentioned basically a good top laner will fast shove a wave sometimes and build up a massive enemy wave that will then hit the enemy at their t ower.
at this point jungler and top laner dive enemy top laner kill him and cause him to miss 2-3 waves worth of gold and more importantly...exp. at that point if the dive is successful the lane is over for the opponent. he is 2 levels or so behind and also in gold. he is just going to be dumpstered once he comes back by a competent player. dyrus says this is why he doesnt need junglers to gank or camp. he needs them to just come at the right times. a good jungler knows when its a good time to dive and when its not.
so look for opportunities.
also I want to note, a good jungler counter ganks. is your laner pushed in to their tower constantly?
they are going to be an easy target for enemy jungler. if you are nearby and about ot back? why not go top sit iin a bush and wait a few seconds for a counter gank. no one shows up? just recall. you were going to anyway. counter ganks are huge part of playing jungle. if you know your lane is about to be ganked you can be there and help them.
if your laner is pushing into their tower all day that means they are winning lane usually. help keep it that way.
granted its not your fault if they get caught out. but its not like you cant do anything if they are shoving.
that is just silly logic.