Modern military trainer aircraft are a lot wider and bulkier than the previous generation. Especially the canopy looks oversized.
Development for these aircraft was started in the late 90s / early 2000s. All of these aircraft have a secondary light combat role. They are supersonic capable.
The seating position is staggered, probably so that both pilots (or student / instructor) have good visibility. This might explain the enlarged canopy. The wider cockpit is likely more comfortable and enables longer missions as well.
Additional avionics and increased fuel capacity may explain the overall increase in volume.
There seem to be some underlying reasons for these designs, but they are unclear to me.
What prompted these changes in the designs?