Why does a person revert to his former condition upon returning from Jamaat?

A brother observes:

' Many raise objections against the Tablighi Jamaat remarking that a person degenerates to his former condition once he returns from the Jamaat. Allow me to ask that if a person after acquiring a certain branch of knowledge remains aloof from it for a number of years, will he be in a position to answer questions pertaining to this branch? Obviously not! Over the years, his knowledge slips into oblivion.
For example, if a B.A student is questioned about standard 8 work, he will be unable to solve it as swiftly as that of a standard 8 pupil. He is in a position to solve the question in a more excellent manner. In acquired secular sciences one loses memory of the knowledge he has attained because of his prolonged neglect.

So the person who endeavours just once in Jamaat and he thereafter relinquishes it for a lengthy period of time, won't the effects of it wear away with time? If he wishes to retain its effects, a close affinity with this mission is imperative. In view of maintaining this affinity, the seniors of Deen recommend that one should participate in the daily Taleem and bi-weekly Gasht programmes and spend 3 days a month and forty days per year in this path inshAllah. Then only will its effects remain or else never. Alhamdulillah, hundreds of thousands of people have successfully put this advice to test. '