Sometimes older, proven technology doesn't necessarily make for a bad choice. Low tech paired with low prices means you can buy in higher volume.
The B-52 which was developed in the early 1950's has gone through upgrades that will extend it's service life until about 2044.
Other weapons such as the M-2 Browning 50 cal machine gun has been around since 1919, and there is no indication that it will be taken out of service any time soon.
Another example is the M-1911-A2 which has obviously been in use since 1911 in one form or another. The pistol, which was replaced by the m-9 9mm Beretta (which was like replacing a new Lincoln with a 1974 Ford Pinto), and is being brought back into service.
New doesn't necessarily mean better or even adequate. If Trump and/or his SEC DEF want to take a look at weapons systems, all i've got to say is "It's about time!"
Even the M-16, which has been in service for 50 years or so, longer than any other U.S. military rifle.
Don’t badmouth the Beretta, it makes a great club.