There are many more elite wrestlers on the planet than elite BJJ athletes. Meaning, more kids start training wrestling and continue competing from age 5 than BJJ. I would guess its somewhere around 10-15 times more. When you have that many competitors who are fractions of a percent different, weight training becomes a huge factor.
Keep in mind also, the techniques in wrestling you can use to win is far less than in BJJ. Wrestlers, by the time they are in their early 20's and have been competing for 15 years already, they know these techniques. They have more time at their expense to train things like strength than BJJ athletes because if you do not know the defense to certain things in BJJ, you will get your ass kicked.
One other thing to consider is that the positions in wrestling reward control. Being able to pin someone or hold them down and break them down, this is absolutely critical and it takes a lot of strength. Pinning and holding down in BJJ is useless and gets you nothing. In fact, if you just hold someone down and pin them, you will get penalized.