So, God, the Prophet and other Imams are incapable of doing these same things?
God can talk directly to all of us but won't. He can send us Angels, but won't. He can reveal all of us divine scripture/books but won't. Isa (a) could've been witness when was taken away, but says he was witness so long as he was among them. God being the true witness in all this, had another witness during that time (Elyas (a)) who is the witness in Bani-Israel that testified to Mohammad (s) per some hadiths in Al-Kafi and gave him the items of past such as staff of Musa (a) and ring of Sulaiman (a) and divine books including Torah and Gospels.
There is a wisdom to emphasize the living have a Guide to be guided by and a leader among them, and the word of light is always found in the best among humanity on earth and the racer of ahead of all in good deeds.
God never has it that current guidance is through dead people. They come and go for a reason. No doubt Mohammad (S) is a light in the highest reality along with his holy family (a), but God connects people to unseen reality through leader of time.
If not, people can argue against Isa (a) and say "why not Moses (a) be the light, we don't need you".
God never allowed earth to be with a proof (living) and doesn't make the connection except through a living one. Mohammad (S) is addressed in Salah but this is through power of Imam Mahdi (A) connecting us to him.
The witness from us is Imam Mahdi (A) while Mohammad (s) witnesses him, and Ahulbayt including Mohammad (s) are presented the deeds every Thursday Night, they are not constantly witnessing us nor emanating the light of God constantly that is a judgment from God - that is Imam of time.