Not every Buddha has affinity with many beings in order to come and deliver them or teach them. Shakyamuni Buddha, has lives after lives, asamkhyeya eons has done a lot benefit to many beings in Heaven as well as on Earth. That’s why when he became Buddha, he had a lot affinity with many people. Therefore, he preached, and they listened. It’s not like if you want to save beings you just become Buddha. Buddha gave his flesh, gave his money, gave his country, gave his wife and children, offering charity all the time, countless of eons, so that’s why when he became Buddha, he was able to preach to these people and they listened.