I am going to discuss about the above issues in three ways,
1st I will tell why people attack you.
2nd i will tell why the above solution are going to ruin the shinobi experience.
3rd I will provide a viable solution for lowbies not having a hard time in the ninja world.
So starting with the question, why do they even attack you? Well thats because in the early stages of alpha, firstly there are no punishments for killing allies, like going rogue, taking away honour points, etc.
Secondly jonins dont protect people untill they run basically inside leaf village, which is easy to encounter by using substitute and running away.
Thirdly, the difference in strength between levels is such that if a person who is 3-4 level higher than you is going to win 100 percent because their melee hit 100 peŕcent of the time while you miss many, and further more the damage you do to higher levels is different from what you do to someone same level as you so you are disadvantageous in four aspects-
1. Health
2. Chakra
3. Stats(i know this doesnt work rn)
4. The dodge, misses and parries
So its very easy for a higher level to dominate the battle against a lower level so they take advantage of this and attack anyone below 3-4 levels of them and seeing who really attacks lowbies at this point are all level 15+ so lowbies do not stand a single chance against them.
Now to answer why this will hinder the experience of a game, this is a pvp game so firstly it doesnt make sense to provide protection till level 10, no enemy will will ever see a genin and "Oh no he is very weak i cant kill him". And this is an early alpha so not many people play right now and if they do then they focus on farming rather than wasting time saving some lowbie who will just respawn in hospital with literally no debuffs. When people have reached the level cap or got the things they wanted they will look to more rp based content like helping fellow leaf villagers and providing them protection, game haa not reached that point yet and people are still busy farming koban or grinding levels. And the last part, lets say you are given the protection you wanted from pvp now what will people do? They will go to the out and to places far from leaf village that may or may not be near enemy nations and grind/farm there while the enemies cant do anything to them. And to the guy above me telling that pvp should get on at level 10, a level 14 will gank you anyways without effort so that solution is meaning less anyways.
Then what can be done to help not ruining the experience for new players? Just make them such targets till level 5 that killing them is of no use to anyone, no honour points, no kill count, no bounty increase, so lowbies will be a waste of time and effort for the enemy.