We can't know this writer's reasons, but a typical reason why someone might use floats vs. ints is that they prefer not to manage the binary-point location and any possible overflows during the following calculations. Instead, they are willing to accept the tradeoff of execution-time vs. programming time, and the increased memory requirements (both RAM and Flash) of letting the floating-point library do it for them.

We can't know this writer's reasons, but a typical reason why someone might use floats vs. ints is that they prefer not to manage the binary-point location and any possible overflows during the following calculations. Instead, they are willing to accept the tradeoff of execution-time vs. programming time, and the increased memory requirements (both RAM and Flash) of letting the floating-point library do it for them.

Update:

Or, as implied elsewhere, the programmer doesn't know how to calculate with integer arithmetic (which to be fair, is a little more complicated than just writing out the formula).