This is the problem with how the game is refereed. When referees are more about 'staying out of the way' and 'doing what football expects', things like this are going to happen. The fact that nobody is appealing shouldn't matter.
But this is what happens when referee is no longer about applying the LOTG impartially but about sports entertainment and promotion.
When we're more worried about 'letting the game flow' than fairness.
It's a clear and blatant foul.
But the culture we have of not penalising this because the defender kept going means that referees actively encourage diving.
Heck, had the defender stopped and stood still in the usual 'shirt pull appeal' the ref probably would have given it! (personally I tend to not give those ones
)