Sensitivities, like muscles, must be exercised to develop. As with any skill, improved sensitivity requires practice, and maintaining improvements is only possible with persistence in that practice.
Talk to a sommelier, for instance. Or a physician.
Or a piano tuner.
Spiritual sensitivity is no different than any other learned skill. Exercise, and it gets stronger. Stop exercising, and it fades away.
It doesn’t even really matter what your definition of spiritual sensitivity is. Maybe it’s empathy — the ability to discern and connect with the emotional experiences of others. Maybe it’s communion with God, whoever and whatever you believe, or don’t. Maybe it’s about an attunement to universal morality, the search for truth, or beauty, or both.
Maybe, probably, it’s some mix of all that and more.
Whatever spirituality means to you, the common fact is that it must be exercised to be developed. When it comes to the truly useful skills, no one gets anything for free.