Database size is often quoted by airline association representatives as being a factor. Your description of how ARINC424 has the potential to confuse pilots is well known by ATC and aircrew alike, and the user interface into the FMS often doesn’t help - I empathise, totally !
I agree that direct entry datalinked coordinates would be helpful, but again many airborne systems can’t accept that and the scale of human change to get pilots to accept a third party directly entering data into the FMS means this isn’t coming quickly either. Though many agree it’s the direction of travel for us all, for this and other reasons UM137/DM40 are used to check what’s in the FMS is correct as it’s quicker, less prone to error (human and ATC loop errors), and provides a faster way to intervene should errors occur. It also provides great data to determine the prevalence and impact of the types of error you described with Gander. This was a solid base is for the mandating of FANS on the NAT, though a solid financial impact analysis also deemed it beneficial too.
Some other food for thought .... ARINC424 manages 30minute increments of latitude and, currently, NAT flights report at 10 degrees of longitude. It’s relatively easy to calculate the number of extra positions that would need to be defined, loaded and tested in every CFP and ATM system. ATC will try to remove organised tracks in future and, generally, make NAT airspace more fuel efficient and predictable to fly in (I’ll try to cleverly add an image posted by Aireon of NAT airspace ... look at all the rhombus shaped black bits ... they reflect airspace inefficiency due to historical flight planning and ATC separation constraints and evidence my point).
Doing this may mean flights report at different longitudes (every other meridian, or perhaps twice as often, and every 5 degrees of longitude), plus new ATC separation standards may benefit from a 15minute increment of latitude too ... so the number of named points may increase substantially with few being commonly used, as they’re all there for airline flexibility. So yI’m could be argued that the problems with naming every point get bigger whilst the benefits of doing so get smaller ... never a good foundation for the business case to change. (Safety is key, we’d all agree too, but I don’t believe we currently have a material NAT safety problem that this would prove to be a/the solution for, so I’ve not argued that point).
if I may offer a personal thought around this .... there are many suggestions that propose ‘organic’ improvements to what’s there already in the NAT that appear logical and practical and seek to be helpful. In my experience, they chase a line of diminishing return as they struggle to keep pace with traffic growth and safety events (COVID excluded, of course). It’s been my experience that finding new, more transformational, ways to achieve the performance and environment needed, rather than tinkering with the old ways, gets better, and more sustainable results. In this respect, leading NAT ANSPs are likely to take things in the latter approach, progressing only the former for short term actions with a quick/short hit is attractive.
I hope this explains why we are where we are ... it doesn’t make other views wrong as I sense we all want a safe, easy and efficient system that helps get us to where we want to go (!)