Then I guess you answered yourself. Its not about caring less in general it about caring less for people who don't care for you or don't care about their issues.
Why to change something good! do you know how rare it is to find caring people!
Instead it would be better to learn to set boundaries and say no for who fall in your criteria without feeling guilty.
To maintain balance and health :-)
For one, it's not healthy to care for people who care less for you.
For two, it's exhausting to care for issues and things that the people who should care about don't.
Why you need to learn to care less?
Yes, it's very easy!! Stop showing how much you care, and bit by bit, in the end you would care less!
Sometimes life forces you to care less, especially if you've been burnt many times, or if you've placed that care where it was not appreciated. In other words, I think a caring person cannot stop being caring in general, but towards certain people or certain situations, it could be a necessity to actually care less.