There were silent Buddhas (paccekabuddha) who did not help others, but only attained liberation for themselves. They had compassion but they did not have the capability to help the world at large.
On the other hand, Gautama Buddha was a sammasambuddha, who was not only enlightened but had both compassion and the capability to help the world at large.
The noble and the conventional sangha of course carries on the propagation and practice of the Buddha's teachings.
As you have rightly surmised, to go with the flow of nature and biology is to go in the direction of embracing craving and clinging, and enjoying sensual pleasures, and trying to become something. Nature and biology also brings the evolutionary drive to reproduce, and minimize suffering, while maximizing sensual enjoyment.
Suffering or dukkha has two meanings, which you can find in this answer. The superficial meaning is literal pain and suffering. And the deeper meaning is unsatistactoriness or discontent. Going with the flow of nature and biology, which is going with the flow of craving and clinging, will never result in stable happiness and security. It will always lead to the general feeling of unsatisfactoriness.
The enlightened beings are compassionate because they see others suffering in the manner described, and want to give them the help they need to become liberated from suffering, but they realize that not everyone wants to become free.
Most of humanity is too deeply entrenched in sensual pleasures and experience the vicious cycle of stimulating craving for more sensual pleasures. The appetite for sensual pleasures increase endlessly. That temporarily masks suffering, but in the long term, suffering is inevitable. So, most of humanity is not interested in liberation from suffering, even if they experience unsatisfactoriness most of the time.
From Iti 109:
This was said by the Blessed One, said by the Arahant, so I have
heard: "Suppose a man was being carried along by the flow of a river,
lovely & alluring. And then another man with good eyesight, standing
on the bank, on seeing him would say: 'My good man, even though you
are being carried along by the flow of a river, lovely & alluring,
further down from here is a pool with waves & whirlpools, with
monsters & demons. On reaching that pool you will suffer death or
death-like pain.' Then the first man, on hearing the words of the
second man, would make an effort with his hands & feet to go against
"I have given you this simile to illustrate a meaning. The meaning is
this: the flow of the river stands for craving. Lovely & alluring
stands for the six internal sense-media. The pool further down stands
for the five lower fetters. The waves stand for anger & distress. The
whirlpools stand for the five strings of sensuality. The monsters &
demons stand for the opposite sex. Against the flow stands for
renunciation. Making an effort with hands & feet stands for the
arousing of persistence. The man with good eyesight standing on the
bank stands for the Tathagata, worthy & rightly self-awakened."
From Magandiya Sutta:
"Now suppose that there was a leper covered with sores & infections,
devoured by worms, picking the scabs off the openings of his wounds
with his nails, cauterizing his body over a pit of glowing embers. The
more he cauterized his body over the pit of glowing embers, the more
disgusting, foul-smelling, & putrid the openings of his wounds would
become, and yet he would feel a modicum of enjoyment & satisfaction
because of the itchiness of his wounds. In the same way, beings not
free from passion for sensual pleasures — devoured by sensual craving,
burning with sensual fever — indulge in sensual pleasures. The more
they indulge in sensual pleasures, the more their sensual craving
increases and the more they burn with sensual fever, and yet they feel
a modicum of enjoyment & satisfaction dependent on the five strings of