The burden is to show why would they stop what Christ commanded.
That is a sidestep. I say that they didn't stop. You are asserting that they lost the power to heal. I see no evidence of this in the Bible. Is it Tradition?
But, to give you a protestant answer, the Bible tells us sufficiently what we need to know. In this case, we seem to know two incompatible things: Christ never abolished miracles, but indeed commissions signs and healing, and the Apostles mysteriously stop.
That's just it, we DON'T KNOW that they stopped. What is your evidence? Did Jesus perform a miracle with everyone He met? Of course not, and that said nothing as to His ability to perform them. Just like the Apostles, in some cases Jesus did and in some He didn't.
Thanx for the ping ... trying to follow along, ‘stayin’ otta tha way up on the porch.’