>>1525095>>1525109Real reason:
Low-level platforms like this are uber cheap to build; just pave om asphalt and bam, you're all set to open for business. However, the ADA Accessibility Law of I think 1990 forbade the construction of any non-accessible station like this, so every new station platform served by high-door trains is either fully high-level, or mostly low-level with what's called a mini-high platform, where most passengers board except during peak hours. However, where trains run with low-door coaches, the "high-level" platforms are barely taller than the low levels for high-door trains, meeting the doorframe instead of the axle of the coach.
The reason why so many stations are still low-level despite being served by high-door coaches is because there are so many of them out there, many of which are incredibly underserved making upgrading each and every one not worth it.
The thing about freight loading gauge clearance is; it CAN be avoided with something called a gauntlet track, which is basically a switch without a frog, shifting the rails over to one side less than the width of the track gauge. CTrail in Connecticut uses them all over the place, specifically at Berlin, Meriden, Wallingford, and Old Saybrook stations, but not New London as depicted in OP's photo, that has a high-level section to the cameraman's back, but most of the platforms are low-level.
TL:DR Some of them have cars designed for them, others it's just cost of upgrading mixed with general apathy
