Why does this happen?

I have been playing chess for almost 2 years and have been improving ever since.I never took chess training very seriously.Having never opened a chess-book in my life,knowing basic theory and only doing puzzles every now and then,I recently peaked at 2200 on lichess.At this point I started training seriously downloading dozens of books associated with strategy,opening theory,endgames etc.Spending 3 hours daily studying chess for the past 2 weeks I have acquired knowlegde and have comprehended a bunch of new for me stratigical ideas.Despite the knowledge acquired not only have I stayed the exact same I have also noticed a huge decline in my overall game.Missing moves that I would not miss before to understanding the demands of the position but being unable to take advantage of my newly renovated chess mindset.Surely I was not expecting to become a Super Gm or get to 2400-2500 but I thought my game would have been significantly improved.Do you know why this happens?

It takes a while to fully integrate and make use of new knowledge. It's not uncommon to actually see slightly worse results for a while during the process. At some point things should get better, with more practice, and you should get at least back to where you were and may see an increase.

When you start studying a lot of new material, it can be overwhelming. Your brain needs time to process and integrate all the new concepts. Trying to apply too many new ideas at once can lead to confusion and mistakes.