It's super easy to implement, comply, and enforce this. Like almost automated levels of easy. It's significantly more complex and requires tons of resources and expertise to go after the whales as you say. Resources they just don't have. Resources that might be wasted if/when it turns out the taxpayer is fully compliant within reason.
It's not about double standards, it's purely logistics and resources - at least on the IRS side. Congress is responsible for their funding, or lack thereof, and it doesn't take long to figure out who's responsible for the lack of it. So I'd encourage you to focus your ire on the response political party, not the IRS itself.