Being healed when the "time is right"?

Why aren't people being healed today like they were in Jesus' day? When a sick person came to Jesus, they were healed completely of their illnesses each and every time.

Nowadays, rather than healings actually happening, most of the time people just spout a lot of thinly-veiled excuses of why the healing ISN'T happening. They say things like "God knows what you really need" and "God will work through your illness" and more commonly, "God will heal you when the time is right. Just keep on believing, even if that healing never comes".

I don't recall Jesus ever refusing to heal someone because "he knew what they really needed". It was obvious what they really needed. And he healed them on the spot. And each time it glorified God.

Why is this? Being able to heal someone on the spot is a sign of a believer (Mar 16:18). Could it be that there aren't many real believers anymore?