I think the point is that for the safety of the nation, Trump should be unaware of where his money is invested and so therefore not make poor decisions for the nation based on how the same decisions would affect his stock portfolio. Obama, whose net worth is a drop in Trump’s bucket, bypassed the blind trust by keeping his holdings in widely diverse, low yield Treasury Bonds, and by making his financial dealings a matter of public record.
Trump has about 550 million more reasons to be divorced from where his money is invested.
But about Obama growing his wealth during his presidency: there is no law that prevents a POTUS from conducting private business or gaining wealth while in office. It’s not about the money. Trump has the same freedom to expand his wealth while president.
The issue is whether or not the way he goes about that is in conflict with the interest of the nation.