They had resources, people, power, soldiers, means ...

So why weren't they able to expand their power, like the Romans centuries later?

first of all, i don`t think egyptians were such good soldiers...=/ that wasn`t their main profession. otherwise they wouldn`t been hiring foreigners to join their forces.

i think the answer is hidin in their phylosophy of life, in their view to the world...

Egyptians created just a kind of sphere of influence on a part of the land of Canaan, on the deserts and on the Nubian region. They didn't show a suitable capability to project their system to far lands.

Romans did it carrying the "civitas" all around Mediterranean Sea. It was possible to "export" the "civitas" since it was based on a very expansive economical/social and administrative system. Ancient Egypt has never shown such a capability [and will] in the long term. To build a great Empire requires the effort of generations.

Egypt had also a main default which was their uncapability to adpt themselves to other lifestyles.Egyptians were very good scientifics and searchers, and they were very wonderful in the research art, but they wouldn't have left , for no reason their way of life. every people on their influence should have live like them,otherwise , it could not walk. they tried to establish their system but their main obstacle, was their religion, and their too centralised power based on one person decisions.
one pharaoh, came out of these way of doing, it was Cleopatrah 7th which, thougt moreand more far than egypt , she was reflecting in a world way domination, by an alliance to the roman emperor, Jules CESAR

Goop point Racine.

It's true that the influence of their particular religion on the structure of the power limited their expansion. Romans considered religion a part, a tool of the "civitas" not the other way round.

I could wonder about Egypt without Sahara. Was it possible for it to expand itself in Northern Africa?

Cultural note about this topic: if we think to the diffusion of the Egyptian icons and symbols ... well we could even say that Ancient Egypt has conquered the world ...

Well, let's not forget that Egypt in its Gold times, was not only the Egypt we know now, it extended to Tunisia and to what is today Turkey on the East and Sudan on South. It was not certainly the biggest empire but if you look in the map, not so small.

Before of Rome really great Empires were more in the conception of their Emperors than in reality. If you compare Sumer, Egypt, Syria, Persia with the extension of the Roman power ...

Thinking to the Sumerian "world map" which included something more than the Middle East, I guess that their idea of "world" was quite "local" ...