First off, neither article is talking about an all-new Bradley. The pic of the BAE one in the rebuilding article is not an M2A4, but a concept BAE is trying to sell.
BAE showcased its Next-Generation Bradley. The concept vehicle...
The M2A4 looks externally the same as an M2A3. The upgrades are pretty much all internal to electronics, engine, and transmission.
Also, the other article is misleading and/or just wrong. Most of the 400+ Bradleys are actually the new turretless Bradleys that are replacing the M113 as part of the Armored Multi-Purpose Vehicle (AMPV) program. The US Army is not increasing its total numbers of A3/A4 Bradley IFV/CFVs. Those numbers will remain pretty constant.
The reason it is not being upgunned is that it isn't needed and it would cost to much to do so. The 25mm Bushmaster is more than adequate for any threat it will face. Additionally, the Stryker Dragoon has a 30mm because that is what the existing Kongsberg Protector MCT-30 turret that was added to it came with.