Indeed Jerusalem had its Essene Gate by the area where they lived in the city. They were very strict and rejected animal sacrifice, as did Jesus.
Why didn’t Jesus tell his followers to be vegetarians? Well, maybe he did. The Gospels of the Hebrews and Ebionites describe a vegetarian ethos: a vegetarian Jesus and vegetarian Apostles, a John the Baptist who ate carob (locust beans) – beans, not bugs – and a rejection of ritual animal sacrifice, be it in pagan temples or the Jewish temple of Jerusalem. The Ebionites were the early Jewish followers of Jesus.
In today’s world there are Jewish vegans and vegetarians. For a Passover Seder, use a roasted beet instead of lamb. Quinoa becomes a main ingredient in many vegan Passover meals. There are plenty of traditional Passover dishes that can be adapted to be completely vegan.
Now the next question: Was the Buddha a vegetarian?