Why am I so bad at chess?
You play too much blitz. You don't think much when you play fast. When you don't think much whilst playing, it becomes a habit to make poorly planned moves. In addition, you need to spend time not just to think about the moves but the themes and ideas associated with them. At the very least play some 10 minute games, and a lot of 15 minute 10 second increment games. I, of course, should follow my own advice more often.
Edit: I just realised that you do play some correspondence. I don't know how much time you spend on each move though. Either way, take into account the idea of playing carefully to avoid hanging pieces and etc.
There are a number of beginner apps from chessking called things like : capturing pieces : simple defence : elementary tactics. Very, very basic, but if you do a lot of them you will hang a lot less pieces, miss less opportunities to take your opponents pieces, miss less forks etc. I did loads of them even though they are very simple in the hopes of curing my chess blindness. Good luck, improving at chess is fun, enjoy the journey.
"..., you have to make a decision: have tons of fun playing blitz (without learning much), or be serious and play with longer time controls so you can actually think.
One isn't better than another. Having fun playing bullet is great stuff, while 3-0 and 5-0 are also
ways to get your pulse pounding and blood pressure leaping off the charts. But will you become a good player? Most likely not.
Of course, you can do both (long and fast games), ..." - IM Jeremy Silman (June 9, 2016)
https://www.chess.com/article/view/longer-time-controls-are-more-instructive
Possibly of interest:
Simple Attacking Plans by Fred Wilson (2012)
https://web.archive.org/web/20140708090402/http://www.chesscafe.com/text/review874.pdf
http://dev.jeremysilman.com/shop/pc/Simple-Attacking-Plans-77p3731.htm
Logical Chess: Move by Move by Irving Chernev (1957)
https://web.archive.org/web/20140708104437/http://www.chesscafe.com/text/logichess.pdf
The Most Instructive Games of Chess Ever Played by Irving Chernev (1965)
https://chessbookreviews.wordpress.com/tag/most-instructive-games-of-chess-ever-played/
Winning Chess by Irving Chernev and Fred Reinfeld (1948)
https://web.archive.org/web/20140708093415/http://www.chesscafe.com/text/review919.pdf
Back to Basics: Tactics by Dan Heisman (2007)
https://web.archive.org/web/20140708233537/http://www.chesscafe.com/text/review585.pdf
https://www.chess.com/article/view/book-review-back-to-basics-tactics
Discovering Chess Openings by GM John Emms (2006)
https://web.archive.org/web/20140627114655/http://www.chesscafe.com/text/hansen91.pdf
Openings for Amateurs by Pete Tamburro (2014)
http://kenilworthian.blogspot.com/2014/05/review-of-pete-tamburros-openings-for.html
https://chessbookreviews.wordpress.com/tag/openings-for-amateurs/
https://www.mongoosepress.com/catalog/excerpts/openings_amateurs.pdf
Chess Endgames for Kids by Karsten Müller (2015)
https://chessbookreviews.wordpress.com/tag/chess-endgames-for-kids/
http://www.gambitbooks.com/pdfs/Chess_Endgames_for_Kids.pdf
A Guide to Chess Improvement by Dan Heisman (2010)
https://web.archive.org/web/20140708105628/http://www.chesscafe.com/text/review781.pdf
Studying Chess Made Easy by Andrew Soltis
https://web.archive.org/web/20140708090448/http://www.chesscafe.com/text/review750.pdf
Seirawan stuff:
http://seagaard.dk/review/eng/bo_beginner/ev_winning_chess.asp?KATID=BO&ID=BO-Beginner
https://web.archive.org/web/20140708092617/http://www.chesscafe.com/text/review560.pdf
https://www.chess.com/article/view/book-review-winning-chess-endings
https://web.archive.org/web/20140627132508/http://www.chesscafe.com/text/hansen173.pdf
http://www.nystar.com/tamarkin/review1.htm