Probably because for most headlight setups, these would "only" be the high beams. While the projectors on the 4th gens use the same bulb for low and high.
I have some of the "other" design, and it seems like it is mostly heatsinking, as the COB itself gets hot at these kind of power levels. So the "bulky" ones have some heatsinking at the end, while the Auxito's rely on the PCB to get heat to the heat sink. Not my personal preference, but it's probably designed to pull the heat properly. Then again, most high beams don't usually get abused as much as lows.
My OE halogen lows were clearly about to die, but the OE highs (after 5 years) looked basically brand new (the actual filament when I upgraded them.)