there must be some big reason for avoiding sexual activity by the early spritual seekers. Despite it being so difficult to abstain from sexual activity. I feel there must be some reason beyond our comprehension? Few impotant reasons are:
1. Sex is ultimate enjoyment one can experince at physical level and it is almost impossible to forget it once you start having it on regular basis.
2. it leads to complicated life of responsibility and one have less time to devote for the cause of spritual practices.
3. It will also lead to lack of concentration while trying to explore the inner world in meditative state.
4. After ejaculation it lead to lack of energy (for spritual practices).