The hmmwv was never designed to be an up-armored vehicle (even in the early 2000's it was rare to see a slantback, let alone an armored unit). But the vehicle had to be adapted to the current situation.
It is great for use in a military setting (think jeep of previous engagements), but it is not good as a vehicle for handling explosives. The design of the truck allows an ied explosion to go up through the center of the hull or the flat bottom under the passenger seats takes the full blow. Because of this design AMG couldn't change the truck to have a V-bottom for the best protection.
Also, the new up-armored turbo trucks weigh 8,000lbs+ over the original trucks. They are more than double the weight of my truck which has the same driveline (I have a lighter frame). My truck's 0-60 is in the 19 second range.
There is also no room under these trucks to add battery packs, etc.
These new vehicles are great (a much needed update), and it's sad to see the end of the HMMWV. However, it will continue to be produced for other countries, spare parts, and as of now $1M/year for the US government. The truck is currently in its 26th year of production (with a civilian run of 14 years) and will probably not wind down until it has passed the 30 year mark, if that.