There is a strong argument that but for the existence of tyrants humankind would have gone extinct before written history. They allowed humanity to evolve and flourish as the social creatures we are today.

While a tyrant does suppress freedoms, and costs lives (in both subjects and opponents) what they provided was stability and strength for the community. This stability enabled ALL discoveries up until, and including democracy. Set aside the luxury of contemporary morality when examining history to understand all its complexities.

Because the powers that be and the systems they have in place (capitalism, Christian white supremacy, patriarchy, cis-heteronormativity) benefit in one way or another.

If they teach us that Julius Caesar was a bad guy and that it's good he was defeated, then we might learn that our current leaders are often bad guys too, and that maybe we should do the same to them.

In the same way that if they teach us that Hitler took his inspiration for the holocaust from already firmly established American racism, we might learn that our own history is just as bad and should be fought against at all cost (which is also what we're taught instead of the reality - the allies fought the Nazis because they threatened their own power, not because of an ideological disagreement).

That's why we're not taught (or only given a palatable token example) about working people fighting the owning class for basic rights, Black brown and Indigenous people fighting the Christian white supremacist establishment and winning, and other oppressed groups standing up to their oppressors (E: nor most of the atrocities they have and continue to commit).

Whitewashing history is always a deliberate act, and is always done in defence of the ruling class.

I think the question really is, why do we glorify people at all? I know that the type of people you mention exist, but I hold them in no high regard. What causes people to admire and even worship others? Why don’t we as a species realize that we all meet the same end, and what causes people to believe that we somehow transcend the inevitable extinction of our species?

Answer these questions, and perhaps you answer your own.

But Alexander the Great literally has the Great in his name.

Historical materialism perfectly answers your question. Quote from On Dialectical and Historical Materialism by J.V. Stalin:

"It is easy to understand how immensely important is the extension of the principles of the dialectical method to the study of social life and the history of society, and how immensely important is the application of these principles to the history of society and to the practical activities of the party of the proletariat.

If there are no isolated phenomena in the world, if all phenomena are interconnected and interdependent, then it is clear that every social system and every social movement in history must be evaluated not from the standpoint of "eternal justice" or some other preconceived idea, as is not infrequently done by historians, but from the standpoint of the conditions which gave rise to that system or that social movement and with which they are connected.

The slave system would be senseless, stupid and unnatural under modern conditions. But under the conditions of a disintegrating primitive communal system, the slave system is a quite understandable and natural phenomenon, since it represents an advance on the primitive communal system

The demand for a bourgeois-democratic republic when tsardom and bourgeois society existed, as, let us say, in Russia in 1905, was a quite understandable, proper and revolutionary demand; for at that time a bourgeois republic would have meant a step forward. But now, under the conditions of the U.S.S.R., the demand for a bourgeois-democratic republic would be a senseless and counterrevolutionary demand; for a bourgeois republic would be a retrograde step compared with the Soviet republic.

Everything depends on the conditions, time and place.

It is clear that without such a historical approach to social phenomena, the existence and development of the science of history is impossible; for only such an approach saves the science of history from becoming a jumble of accidents and an agglomeration of most absurd mistakes"