Often, when you lose lane, you get told to "farm under tower" or "stay under tower" which is some solid advice, apart from it having a few flaws. Most of which being able to be changed by Riot, only one being mechanic based.
Tower is not a safe zone
Tower has never been a safe zone
Aside from the fact the enemy laner can freeze the lane half way in to prevent any XP, here's the reasons why it doesn't work.
Some champions have two dashes
Some champions can dash into you, and then jump over a wall
Some champions can wait for a minion wave to come before dashing across on a 0.1 second cool down
Some champions have abilities longer than the actual tower range itself
Towers do not slow
Towers do not do enough damage
Some champions have resets on long dashes
Some champions have invisibility
Some champions have invunerability
Some champions have healing abilities
Some champions have global ultimates
Tower can barely kill one person, let alone able to kill two that push in
Need I go on?