Everything fades away

Languages
Langues
Lenguajes
Езици

Those are the four ones I believe I have a good knowledge of: Bulgarian as native, English, French and Spanish.

I love languages. I lived them since I started talking.
I remember when I was three I used to open the world atlas and point at Paris and say: 'I wanna live there'. Hence when I was five I started learning French. A very beautiful language, loads of fun while studying it. 10 years late I decide to venture in another language.

Here came Spanish. Very tough studying it, as I had thousand and thousand hours per year and studying stuff as biology and chemistry in Spanish, which was ultra fascinating. :)

Then came English. I had a really bad start with it, where I really disliked it and didn't want to learn it whatsoever.
But changes in direction of where to study, I had to learn it well and quite quick. So before 2007 I had 2-3 years to go through 4 years of material.

Back to the title.
Why everything fades away? In term of languages you have to practice them as otherwise you waste years of studying.