Well, to be perfectly honest I don’t think there are too many people out there who jump for joy before heavy strength training days. It’s hard work and most of the time it’s easier to just say “meh” and do something more fun with your time.
The thing is, while you may not like the activity itself, you do like the results that the activity brings. You mentioned that you love to pitch, so I am going to assume that you particularly enjoy pitching well and being as effective as possible. If you don’t train in the offseason, then you will not do as well as you are capable of doing.
So basically what I am trying to say here is that there is no magic pill. You wont find some “thing” out there that will give you motivation to push through all the pain and sweat to succeed. The one weapon you possess is staring back at you from the mirror. The best athletes in the world are the ones that are willing to push themselves past what is comfortable or easy.