Thanks for that information.
Some of those points were surprises e.g. the first 2 drives were internal, and were also different makes / models from each other. Unfortunately, since they are no longer available for further testing or collecting their SMART data, I doubt that any conclusive answers for their relatively short drive lifetimes can be established.

I forgot to ask about your other drives (as I hadn't guessed that any of the problem drives were internal, when I replied previously), but you mentioned that your OS is on an SSD and you have a "recorded TV" HDD. Since SSDs have some different causes of failure than HDDs, this does not help to eliminate much from the range of possible causes of the premature failures. That leaves the "recorded TV" drive, as the only HDD which I think you are saying has not failed within a year.
One of the common factors appears to be the internal power supply of that PC - obviously it powered those 2 previous internal drives, and it also powered the external My Passport drive via USB. Just because the "recorded TV" drive has not failed prematurely does not
prove that everything is OK in this area, however this isn't top of my list of suspects.
I'm not familiar with that Silverstone PC case (a quick Google seemed to show some different variants of that model), but one area to check is whether any drive slots get reduced airflow, and so those drives run hotter. Again, without the SMART data from the 2 previous internal drives, we don't know whether those drives were getting hot.
There could be (unusual) environmental factors, but overwork (overheating too?) is the biggest concern for the first 2 drives, considering the limited duty-cycle and power-on hours which drive manufacturers use in their specification for normal (non-enterprise) drives. Since those 2 drives failed each within a year, were you able to RMA them?
I think you are saying that the 3rd (external) My Passport drive has been doing less I/O, than the 2 previous internal drives were doing. However it's easier to overheat drives in external enclosures without fans, than internal drives in a ventilated PC case. Let's see if the available SMART data gives any clues. To collect that, you could download HDD Scan (free) from
http://hddscan.com. Use that to read the SMART data from the WD My Passport
and from your "recorded TV" drive. You can either save those 2 sets of SMART data as files to your OS drive (and then attach those files to your reply), or you could take photos of the SMART data being displayed on the screen (and attach those photos), or you could take Windows screendumps of the SMART data being displayed.