The three guys who have to carry around the old M2s might disagree with you.
I understand that, but the M2s were in short supply during Desert Storm and they were a real game changer. If making them lighter means that fewer of them will be deployed, it's not a good trade off.
We used them as vehicle mounted systems and for defense, so the additional weight wasn't a real disadvantage.
I was on a project for the navy that was working on a replacement for a munitions trailer. Everything was going according to plan until the Navy decided they wanted them made out of titanium instead of aluminum. At that point the cost skyrocketed. Titanium is harder to machine and more expensive than aluminum or steel. The Navy ended up cancelling the project due to the substantial additional costs.