They had an internal issue that needed debugging and so they decided it was easier to just disable it all-together for the holidays. This is less an indicator for complexity and more an indicator of apathy. An ipv4 issue would have obviously prompted a much more swift response. In fact considering this is reddit, I'm surprised this hasn't happened more often considering they seemingly go down every other day regardless.

The only ones making this hard are apathetic engineers who keep kicking the can down the road for the next generation. Arguments against ipv6 are like sailers on a sinking ship bickering with the rescuers that while the ship is completely underwater at this point, they can still float on their backs for a day or two, so their help is unecessesary.

IPv6 is inevitable, you can either deal with it now while it's hard, or deal with it later when ipv4 addresses are too expensive and your infrastructure is already so entrenched that transitioning is a nightmare. The latter is the situation Azure & GCP are slowly finding themselves stuck in, and they have only themselves to blame.