Well ... there are a couple theories for this.
Buckling springs have lower resistance at the start as well...so your fingers have momentum and their own weight helping you on the way down. Topre starts off at 55g.
That's why comparing switches with different force curves is difficult..you can't just just look at peak force...
Same reason why Browns, which peak at 55g seem lighter to me than 45g Topre...if I press them slowly, Browns will take more force..if I'm typing, they feel lighter.
Not to mention you just get used to what you're using...