It just depends on the lane.
Top lane is largely about wave management. Typically unless you cross the river you are unlikely to get ganked.
Tower dives typically only occur when:
You are really low on health, mana, or both
The tower is low (less than half health). This means you have probably been laning for too long (bad players lane forever but surviving tower dives is easy in the post 15 minute mark.
If you do not control your jungle - once you lose control of you jungle dives are more likely to occur
I also think a lot of low elo players use the term "gank" too loosely to often describe a death. Ganks occur during laning phase when one or two opponents rotate to your lane to kill you. Laning typically goes on for about 10-20 minutes or until about level 7-10 maybe. Sometimes it last longer if you have a split-pusher on your team. But in general laning phase "ends" as do "ganks" after the first tower falls.
Calling a rotation to your tower at the 20 minute mark a "gank" is not really accurate. At this point in the game laning phase is over, even if all the towers are still up and lower elo players will complain about "the lack of ganks" when people are level 10. Then they will blame others for their deaths, but the reality is that what a lot of players will attribute to as repeatedly getting ganked just means that the mid game phase is beginning and this is where people need to group and give up laning.
Laning phase is just to level up until you are strong enough to enter the mid game phase. In general, laning phase shortens the higher in elo you climb.