Lin Tian had his reasons for giving it to those few people.
First, Lu Ya and Great Emperor Fengdu were a late Quasi-Saint and a peak mid-stage Quasi-Saint respectively, and both had helped him. Giving it to Lu Ya was a way to recruit him. After all, Lu Ya was alone and had chosen no side. With a little incentive, he would probably be eager to kneel at Lin Tian's feet.
Moreover, Great Emperor Fengdu had voluntarily joined the Heavenly Court under his command. Granting him a strand of Hongmeng Purple Qi could serve as a reward!
Holy Mother Jinling and Taiyi Savior Heavenly Venerable were important figures he had appointed to hold positions among the Six Sovereigns. Both were Quasi-Saints and his subordinates, so they too deserved this gift of Hongmeng Purple Qi.
As for Holy Mother Wudang...
She was an outsider.
Lin Tian gave her a strand to tell everyone present that he treated everyone equally.
As for not giving any to the Three Skies, Grand Supreme Elder Lord, and the others, he also wanted to make it clear that those who were not his people should not expect to obtain it so easily.
After a moment, Lin Tian said slowly, "Those five bear fortune and blessings, and their karma is entwined with mine. At this stage, they are the most suitable candidates to bear Hongmeng Purple Qi. Those of you who received none need not lose heart. Many among you possess the potential. When the time comes, I will not be stingy. I have no shortage of Hongmeng Purple Qi. You need only devote yourselves to comprehending the Dao."
"We obey the decree of the Vine Dao Venerable!"
The immortals bowed, all but saying, "Vine Dao Venerable, we are yours from now on. Give us whatever orders