One reason why animals produce so much more sperm than eggs is that a sperm is vastly smaller than an egg, so males can afford to produce many more. But they don’t do it just because they can.
Small, mobile sperm are good at seeking out gametes, and large, well-stocked eggs give them something worth seeking out.
It’s a fundamental distinction between the sexes and part of the reason why it tends to be males who put the effort into courtship and fighting off rivals. If a female mates with more than one partner, competition continues within her.
The more sperm a male produces, the greater the odds that one of them will reach the target first. The competition is fierce. No wonder a single ejaculate from a bull contains 10 billion sperm.
And for another sperm fact, did you know male woodmice have remarkably co-operative sperm? By hooking together in trains of hundreds or thousands of cells, they are able to swim faster than single sperm. Now that's teamwork!