It’s totally up to you if you can/want to invest the time.
Envato are successful because they control (more than other marketplaces) the quality and quantity for sale hence why basic or rushed items don’t make it through.
It’s a reasonable requirement to join the biggest and most active marketplace and while you are right there are other options but none that come close to comparing to Envato in terms of size, potential, etc.
If you are submitting this as an HTML template and just sending jpg then it is probably not even being reviewed at all and hence the auto hard rejection.
Beyond that, with respect, there are numerous freebie templates online that offer similar designs/features, etc.
You have got to bring premium features, functionality, versatility that warrant someone wanting to pay for it.
There will be people looking for minimal design - that is no excuse for not having many more original elements and features included that they can choose from OR applying an original design to the look and feel