Why is that the sheet modules or "microsoft excel objects" expands
when I switch from the VBE to Excel?

In one project, I have 50+ sheet modules, which I keep collapsed while
working in my normal modules. This way I'm not distracted by all the
sheet modules when scrolling to other modules. I then switch over to
the Excel workbook to work in the cells. When I switch back to the
VBE, all the sheet modules are no longer collapsed. I have to keep
collapsing them when returning to the VBE, they won't remain
collapsed.

Is there any way to prevent this?

Thanks.