You have to consider the weight classes, like Floyd Mayweather is like fighting at 145lbs, what weight class are you watching in kickboxing.
Actually a lot of it has to do with efficiency. Boxers only use hands, and must not blow all their energy otherwise if they have no more gas/power left in their hands, they will almost certainly lose if they gassed their arms out. So they have to conserve a bit more energy and causing dodges/evasion to be a good part of the success in boxers.
In Kickboxing, you can use your legs for kicks which limits a lot of ducking and head movement directions because they can get caught easily with a knee, upkick, or just a roundhouse kick to the head if they choose to bob their head. Kicks are stronger than punches, about 2x-3x more power. They set up with kicks to the leg, and if a kickboxer becomes flatfooted because their leg or thigh is damaged, they receive more power transferred to their head. This is because they cannot pivot or divert the punch/strike.
Or a more easier view is that boxing is 1dimensional, and kickboxing is as much as 3x the game of boxing. More methods of finishes. More setups are available, more choice of angles, making it harder to predict or see strikes coming as to boxing which you can only expect punches. Ultimately, some have compared boxing and MMA, and that MMA has way more methods of finishing a fight than boxing does, and so statistically speaking and mathematically logical we should expect more finishes in MMA. In my opinion, there would be a higher finishing rate in UFC if they used a square ring instead of a hexagonal cage.