The first number denotes the kernel version.
The second number denotes the major revision of the kernel version
The third number indicates the minor revision of the kernel. It is only changed when new features or new drivers are added
The fourth number, if present, represents corrections, such as security patches and bug (i.e., error) fixes.
here is an example of a Canonical/Ubuntu Kernel
linux-image-5.4.0-73-generic_5.4.0.82_amd64.deb
So 5 is the main Kernel, 4 is the major revision of 5 the main kernel, 0 is the next minor update, 73 is the ABI number it is an ever increasing revision. It basically denotes how many uploads have been made for this kernel version
so basically Canonical/Ubuntu used kernel 5.4.0 and revised it 73 times since it began
Some problems with kernels are caused by bad drivers or bad code and the like or new drivers and patches get released - as more and more devices hit the market with ever changing hardware it is no wonder the updates are accelerating