If the Force is hereditary, why not breed Jedi? Then there would be more Force sensitive people to become Jedi.
Hmph! Makes sense to me. But to more specifically answer your question, it's rooted in principles and dogma of the Jedi. Breeding typically involves two things. Firstly it's often the result of romantic love between a male and female and... Okay you know this stuff!... The point is that such a relationship often centers around long-term and growing romantic feelings which the Jedi would regard as a form of passion. The "theory" the Jedi hold to is that these passions would grow eventually leading to a level of attachment (and possibly fear of loss) that would create dark emotions under the right circumstances. And that would be a path to the Darkside.
Secondly the sexual aspect of breeding is built on arousal and indulgence of passions. Again the Jedi feel that nurturing such passions are dangerous; possibly leading to jealousy, greed, or fear of loss. And those things are paths to the Darkside.
The Jedi teach to forbid passion. The Sith teach to embrace passion. Are you aware of their "Codes" from the old EU?
The Sith Code:1. Peace is a lie. There is only passion.
2. Through passion I gain strength.
3. Through strength I gain power.
4. Through power I gain victory.
5. Through victory my chains are broken.
6. The Force shall free me.
The Jedi Code:1. There is no emotion, there is peace.
2. There is no ignorance, there is knowledge.
3. There is no passion, there is serenity.
4. There is no chaos, there is harmony.
5. There is no death, there is the Force.
These codes existed throughout the old Lucas Star Wars Expanded Universe. I'm not sure that Disney is using them as canon now. But the point is it gives a guideline of how the Sith and the Jedi regarded forms of passion; what their philosophy was on it.
As for me myself, I always held that this was one of the flaws of the Jedi. I clearly made my viewpoints known on passions surrounding breeding, sex, and love in my quotes from KOTOR (Star Wars: Knights Of The Old Republic) as stated below:
"Love doesn't lead to the dark side. Passion can lead to rage and fear, and can be controlled... but passion is not the same thing as love. Controlling your passions while being in love... that's what they should teach you to beware. But love itself will save you... not condemn you."
―Jolee Bindo, to Revan, when discussing love
Well I better stop talking now. My mouth has been open so long it's starting to draw flies!