Jainism was spread and made popular in India by Lord Mahavir who was the 24th guru of Jain religion during mid 6th century B.C...

One can find this community more towards North West and western part of India.
Jainism is governed with the ideas of Non Violence called Ahimsa; Mahatma Gandhi has been influenced greatly by this philosophy and in turn influencing Martin Luther king to resort to non violence.

Jainism takes non violence to a very strict level and respect life at any level including plant life. That's one reason they don't use root vegetables (onion, garlic, potato, carrots, beet) in their cookery as it harms the plant. and you can find good use of tomatoes in curries and gravies .
Food which contains even small particles of the bodies of dead animals or eggs is absolutely unacceptable. While milk(!) consumption is not forbidden under Jainism.

But in India almost everywhere milk is used as vegetarian dish. Use of honey is also restricted.
So one can imagine the difficulties a chef in any indian restauant has to face to cater them when at the same place you will get non vegetarian dishes as well.

There are instances when I have to suggest some dishes out of the menu to them , and believe me its not an easy task.

If we talk about Italian , french or even a multiregional indian cuisine you will find the use of onion and garlic extensively and you know the taste of it.

Try suggesting some dishes deprived of Non veg, onion garlic, carrot , potatoes , radish or any root vegetables.

If you find such restaurants in your place , try it and you will understand what I am saying.