Azure’s main feature is that it’s not connected to Amazon retail and they’re committed to Windows. So their clients are often in it for the long haul good or bad, those who can switch do.
I used to do $100,000 a month in revenue on Amazon with one HP skew. The product grew to #1 in its category within a couple months, another month after which Amazon started selling it to, "shipped from sold by Amazon".
Amazon is happy to help be your growth partner until you prove worth devouring.
AWS is their most profitable business in terms of margin. It makes sense to avoid funding your competition if possible, which is a problem for Amazon given how many business divisions they have and continue to add.