It’s because not enough countries play it – well, not enough countries at a high enough standard to warrant it being an event anyway.
The fact is that cricket is only played at Test level – that is the highest level – by countries that used to be part of the British Empire.
The only Test playing countries are England, Australia, South Africa, the West Indies, India, Pakistan, New Zealand, Sri Lanka, Zimbabwe and Bangladesh.
It simply wouldn’t be fair on all the other countries in the world to compete at cricket in the Olympics!
That said, there was once an Olympic cricket match. It took place in 1900 and a club team from England beat a team of British men who were based in France and were representing that country.
England won and can therefore claim to be the current Olympic cricket champions.