Why, do we need to use, "Malwarebytes"

I keep seeing the advice in this forum to, "run malwarebytes". which brings me to the following

.

1 What does 'Malwarebytes' do that Norton cannot.

2 What are Norton doing to make their Security Program robust enough so that Malwarebytes is not needed.

 

As this is all to do with the security of PC data, I feel that Norton/Symantec should be working towards becoming the " 'Total' Security Protection Company", where there is no thought of needing or using other Prog's to rectify security problems.

 

I'm fully aware that I might get a few 'kick backs' here but felt that I had to ask.

 

If I'm barking up the wrong 'Tree' here, I'm sure some of you will put me right.