Why do today's Christians blv they're born again & QUICKENED in water baptism but have none of Jesus' promises (Acts1:8;Mk16:16;ICo12:7-10)?

I do have the promise that was associated with being baptized in the name of Jesus Christ!

That promise is salvation, forgiveness of sins!

 "He that believes and is baptized shall be saved." ( Mark 16:16)

 "Repent ye, and be baptized every one of you in the name of Jesus Christ unto the remission of your sins" (Acts 2:38, ASV)

 "...be baptized and wash away your sins..." ( Acts 22:16)

Cornelius was told Peter would speak "words by which you will be saved". (Acts 11:14 ). What words did he speak?  "He commanded them to be baptized in the name of Jesus Christ." This baptism required water. ( Acts 10:47-48)

You often mention 1 Corinthians 12 that speaks of the manifestation of miraculous gifts, but you often ignore chapter 13 that speaks of the duration of those gifts, and chapter 14 that has regulations regarding them.

Without all three chapters, you don't get the full picture of the manifestation, duration and regulation of those gifts.

You Also often mention Mark 16:17-19, but often neglect verse 20 that indicates the purpose of those signs and the fact those promises were fulfilled.

Promise of the Holy Spirit fulfilled in Acts 2, in Jerusalem, to the apostles as per John 14-15-16.  Fulfilled and not repeated.  The next involvement of the Holy Spirit gift is the command to be obeyed in Acts 2:38, which is repeated over the centuries.  A world of difference between the promise fulfilled and the command to be obeyed.

1 John 4:1 

Beloved, believe not every spirit, but try the spirits whether they are of God: because many false prophets are gone out into the world.