Consider the minority versus the majority.
The majority of this country are white-british, lower- to middle-class. Johnson is known as a wrong 'un, his comments are, sadly, to be expected. They aren't electoral issues unless the opposition are strong enough to make them stand out. The electoral impact of Windrush, for example, was clearly minimal. As was Grenfell, as it was deemed a wider field beyond the Tories for blame. The impact it has was towards ethnic minority votes where the Tories are traditionally weak anyway. The PM not laying into the monarchy is just expected.
Very little Johnson does wrong is of impact to his base - consider Theresa May attacking the triple lock on pensions and the impact that had on her electoral success as an example of what does impact the Tory base.
Whereas Labour are standing in front of the hammer and sickle, stubbornly and bewilderingly refusing to acknowledge common sense definitions of anti-semitism, taking a knee in support of an extremist movement, treating the public like idiots by taking part in stupid photo ops during a pandemic and so on. These are all things that the majority will take electoral issue with, particularly Labour's support base.
When Biden took on Trump, he gave him the rope to hang himself. Realising Trump's response to COVID had killed him, he simply avoided own goals. Labour don't do that - they create numerous own goals of their own to compensate.