The reason is just digital input really. Pinyin and Romaji typing have become so common that a lot of people write Hanzi/Kanji by hand less and less and it's so complicated of a skill there's really no other way to get it in your brain other than practice. I even notice it myself, I easily recognize 10x more characters than I can accurately write.
Because shrimp meat is something I see written out EVERYWHERE.
It just seems like such an odd outlier example. Like talking about a friend that spells "been" as "bin." I'm sure it could happen, but it's not indicative of a broader trend.
The story was reported by Victor Mair, though, who is extremely opposed to using characters and often exaggerates the issues with them.
Personally, I've seen a lot of Chinese people's written notes, and I don't think I've ever seen them resort to pinyin, even among people that didn't go to college. I just asked a few Chinese friends about this, and they told me they never resort to pinyin either.
I actually did a deep dive into the issue of unfamiliar characters coming up when reading, and how people handle them. I won't go into all the details, but the general takeaway is:
1. Unfamiliar characters can actually be quite rare or quite common depending on the material you're reading.
2. It's not much of an issue for people either way.
Of course, you _can_ escape to Hiragana if you're so inclined, but then you would show that you don't know the character - so it's just avoided.
Ambiguity is king in Japan.