Parts availability starts to get weird. Wear items are usually available regardless of year like filters. After 20+ years, big vehicle specificitems like axles tend to be less common but still usually available as aftermarket parts, but not from OEM like suppliers for normal prices. Anything older than that, it gets dry if it's a normal car. Enthusiast cars have a better aftermarket but that's not always the case.
I do agree on repairability but repairability is moot when you can't get good parts.
I also agree on the DIY aspect.
Also it really depends on the gearbox. VW sources either common Aisin automatics or makes their own (manual and DSG). The aisin gearboxes can be treated like Toyota gearboxes and can use their fluid. My Passat has a Aisin TF60SN gearbox. I can use the same fluid for that as my Toyota Sienna (it's an 08 so it takes the same WS fluid instead of the dex iii or T-IV).
The TF60sn is bad for other reasons but not entirely VWs fault.