You ask why anyone would worry about living in the tribulation, since
we are part of God's kingdom already, and have that inner strength
(paraphrasing you).  However, to me, the trib is very frightening
because of the mind control which will then occur.

In ages past, martyrs simply had to suffer and die.  Bad enough.  But
in the trib, Big Brother will brainwash you.  He has the scientific
means to bend your mind to his.  If God does not wrench you out of BB's
control, you cannot keep your mind fixed on God.  You have lost inner
control.

We see how people can already be heavily manipulated by drugs.  Not
merely "street drugs" but by the myriad of  pharmacy drugs. 
Psychotropic drugs such as anti-depressants, anti-psychotics,
stimulants, calmatives, anti-anxiety drugs, Gaba-inducers such as
Lyrica and Gabapentin.  Shock therapy alters parts of the brain.

Some of these drugs are really useful, especially those which control
seizures, so they are not all bad, but  we know that the mind can be
controlled by science.  And new electronic mind control is being
developed all of the time, and has been for many decades.

So only through God's intervention will anyone be able to maintain his
inner mind strength.  This intervention would seem most reasonably to
entail forcible removal from the situation, i.e., rapture or "calling
out",  but of course God can do anything, and could enable a person to
maintain inner balance even in brainwashing.   God can do anything at
any time, so it will be His call how to save his sheep's minds from the
overpowering by Big Brother.