The very simple version is that the newer versions support faster speeds.

It's more nuanced than faster speeds. All newer versions of WiFi came with speed improvements but compared with previous versions WiFi 6 speed improvements were comparatively modest. The advantage with WiFi 6 over its predecessors was a focus on improving latency and reliability. The number of supported clients was drastically increased with the implementation of technologies first developed in cell networks. Wireless antennas used to be limited to serving each client one at a time. Now they've been given the ability to multitask.

You can liken it to a restaurant where the cook is the network, the waiter is the wireless antenna, and each customer is a wireless device. With WiFi standards before version 6, the waiter was not very good at their job and once they collected an order, they would give it to the cook and wait for the cook to finish cooking the entire meal before delivering it to the customer and moving on to the next customer. This method was improved in the past by making the waiter quicker which is where we get the speed boosts. You can also improve on this by adding more antennas or "waiters" to the environment but the waiters themselves are still not operating as effectively as they can on an individual level. This is why WiFi 6 is such a major improvement that flies under the radar. The improvement may not be that noticable in a home environment where the antennas only have to serve a limited number of clients but in an environment where hundreds or even thousands of clients are communicating simultaneously, this is a critical improvement. On top of this, the improvements have decreased the rate of packets being dropped and improved latency so even in home environments, a network running on WiFi 6 will be more robust and reliable. WiFi 7 will go back to the old paradigm of significantly increasing speed once again.

Lots of really cool little things that add up to making it faster

https://youtu.be/j5egLKTwOt0