Sure, Force descendants don’t always happen, but I am saying that they never happen, or at least there is absolutely no causal mechanism (and certainly no Midichlorians to be passed down). For me, the Force is either present mysteriously in a person, perhaps for them to fulfill some feat or destiny, or they have dedicated their lives to cultivating it in themselves and/or have an unshakeable faith in the Force which gives them their power.
It often happens that a person can temporarily gain ability in the Force to do something usually beyond their abilities, and this is where ‘May the Force be with you’ comes from in common parlance. In these cases, the Force doesn’t necessarily persist in that person once their destiny has been fulfilled.