And most importantly, integrating new things that are even in theory this simple, costs tons of money and time because anything new will require some sort of operational evaluation. Just because a newer, cheaper, more cost-effective replacement is out there, doesn't mean that we can just slap it into our aircraft and call it good (even if it does end up working just fine after installation).
Take my aircraft for example, a mid lot F/A-18C......with upgraded mission computers (even 10-15 yr old ones for that matter), we could do a lot of things that we can't do right now, that other newer aircraft can. We could also have a civilian ILS, and thus not rely on TACAN approach mins for alternate filing purposes (not to mention the extra peace of mind). We could get certified for GPS approaches if we had the ability to store the GPS wypt database in our jets in it's entirety (vice the 59 programmable waypoints, 10 marks, and ~200 stored GPS points that we currently have). We could also be RVSM capable with a few simple mods. Not to mention that there are additions that could be made in a pretty straight-forward manner that would help us out tactically.....even some things that have been developed, tested, and then benched because of lack of project funding. Just a few examples of things that relatively cheap technology could do for us, if it didn't require expensive contracts, and years of operational testing to ensure that it would continue to work in combat, and flying on and off the boat (a pretty rough environment admittedly). I'm sure the CG shares some similar concerns and acquisitions problems.