I think the biggest issue isn't letting kids use a tool, it's getting kids to do the work.
I recently worked with a bunch of kids in college, all stem majors, who couldn't Google effectively or do basic math in their heads. It's not a matter of "don't let them use a resource" it's that many people won't try.
Limiting technology isn't cruelty, it's vital for learning many skills. Number sense can't be taught by a taking a picture and writing an answer.
What exactly should be done to motivate?
I ask because schools do a lot to motivate but kids often dismiss it as lame or complain about the efforts. It's very easy to say "motivate kids" but actual ideas aren't common.
Let me give you an example, everyone has heard "when will we use this in real life?" in math class. The same people asking those questions are the same that groan at word problems. So you have kids complaining that won't be able to use something in real life, and upset when they have to solve a real life problem. What's the real complaint the student has? They have to try.
I agree that so much more can be done to make school fun, but it's not all on the teachers. Students have to be present, participate and willing to leave their comfort zone in order to have better results.