Why is Johnson more popular than Starmer?

It's much subtler and pervasive than that. Johnson is an extremely intelligent manipulator. Unless people understand or try to understand how narcissistic sociopaths operate, they will never understand how they have been fooled and why. He does not care about people. He has no capacity to do so. His interest in people is how far they can be used to achieve his own ambitions. After that people are nothing to him and can be discarded. The majority of people who voted for Brexit and voted to keep the Tories in power in 2019 were over 65. And yet when Covid struck, he was happy to let elderly bodies pile up. The modus operandi of the narcissist is court, devalue, discard. It happens in personal relationships and it happens in politics.

Something else is at work too. Cognitive dissonance - the mental discomfort that results from holding two conflicting beliefs, values, or attitudes. For example, you may believe in law and order and that the party you support stand for that. Then you find that that they are exploiting the law or outright breaking it. That makes supporters uncomfortable.

There are various ways to try to cope with the discomfort of cognitive dissonance. One is to seek scapegoats, blaming other people or outside factors. You see it here all the time - blaming other political parties or personalities when the party that is failing the public has been in power for twelve years. It's illogical but the right wing press play to this by finding scapegoats that those experiencing cognitive dissonance can latch onto.

In very simplistic terms, I see it as no different to a personal relationship. Do you dump a lying, cheating, abusive husband or do you tolerate the abuse because you once loved him and cannot gather the courage to leave? Do you blame him for lying, cheating and abusing or do you find excuses to explain his behaviour to vindicate your own decision to stay?

Starmer is weak. All he does is moan about the Tories. I’m a paid up union member and I’d voted for Lisa Nandy, she should be handed the reins.It’s like currently he’s banging on about the Windfall Tax. So, fine, that’ll cover this year. But time and time again in interviews he’s asked what he would do in the following years. But he won’t answer! He’s still not solved the antisemitism problem in the party. Where are Labour’s policies? They sometimes talk about what they would do but don’t back it up with how they would do it. There’s no way I’ll be voting for this sorry shower. They are a shadow of the Labour we used to know and trust.

He isn't.
Also Johnson isnt a bad boy he is a very damaged man.

According to every opinion poll since at least January, he isn’t.