This is because there actually is a calculation that people do between "effort" and "love" (it's not some 1:1 ratio and you can't calculate it, it's real). At least for the vast, vast majority of people with functional interpersonal skills...
It's the difference between calling your mom and just saying "Hi mom, this is me thinking to call you. bye." vs calling her with a prepared thing to say/ask about that you had to take extra time to think about before calling. Effort went into that. You don't need to tell her "HOW" you came up with what you wanted to talk about, but there is a difference in how your call will be received as a result.
If you really believe that sending a text versus a hand written card will have no difference on how the message is interpreted, you should just know that you are in the minority.