What are some reasons why scientists predict that niagara falls will be gone is 50,000 years?

Erosion that occurred in the past has led to the present-day location of the falls with the Horseshoe Falls in Canada and the American and Bridal Veil Falls in the USA. Historically, the rate of erosion of the falls has been around 3 feet per year. During the last 12,300 years, it has eroded 11.4 kms. The Niagara Falls has retreated from Lake Ontario towards Lake Erie in the last 200 years at a yearly rate of 5 feet. However, since 1942, the rate of erosion has reduced. Due to remedial efforts, the current erosion rate has come down to about 1 foot per year.
Erosion is the reason why Niagara Falls may be gone in 50,000 years.

The mass has escaped into a gas which you can not see so the law stays true.