Just because he wrote some code that was used so widely doesn't make him more significant than a janitor who cleans after you, or the "gang" member who was evading the brutal cops for a chance for his freedom. The sooner we realize people are equal because they're human fucking beings the greater hope for humanity to avoid its imminent demise.
It's like asking what makes 5 greater than 5. Humans are all significant simply because they have rational minds and are rational beings. A human being cannot impose on others a value or worthiness, because we are rational beings and have independent minds. As you probably have noticed by now this is not me saying these things, it's from Immanuel Kant. I found these lectures on the topic absolutely amazing to watch: https://www.youtube.com/watch?v=kBdfcR-8hEY
It's worth mentioning that all humans are -humans- just like 5 == 5.
However, the fact humans are humans doesn't make them equal. Unlike a number humans have dimensionality. They can be taller, shorter, stronger, weaker, smarter, dumber, richer, poorer etc. Along with any number of other attributes like job, geographical location, father, mother etc.
Equality is a very precise thing and humans are anything but equal.
You need to read some more philosophy (or, I guess, watch some more.) By asserting unconditional equality, you deny the existence of the will. That position can be defended, but I'm skeptical that you're up to the task at the moment.
Because life is random and stochastic. The sooner you realize that your very existence was simply a roll of the dice, the more liberated you will become.
Don't be too sure - some of histories supposedly greatest people have also been mass killers. Your views on them largely just depend on which side of the conflict(s) you were on and what time you are in. To take a fairly simple example, Churchill. Lots of good, lots to admire. But plenty of dark decisions and many deaths attributable to these.
Because you never cared about non-great ones. Observer bias.