I'm not upset by your opinions because that's exactly what they are, there are many people who like flappy bird or it's derived clones.
So it's debatable that most people consider it to be shit.
Doing a remake of what you consider a good game is ok, but equally that also shows no imagination,originality or creative thought.
So what it really comes down to is that you don't like the game which is fair enough.
I think the effort of making a flappy bird clone on an old machine depends very much on the skills of the developer.
Some might of made the game in a day and so spent little effort, so why not make it?
Others might take longer because they have never programmed on a system, as so it's a learning experience that takes more effort.
But that longer time is not effort wasted if they learned something that can take on to make something more original in the future.