What can we learn from bringing back Martian regolith instead of testing it onsite?

In this week's episode #1018, NASA's plan to revamp the Mars Return Sample program into something cheaper and faster. And yet the costs of the programs the linked article discussed start from $5.8 BILLION.

From what I Google, the sample tubes hold up to 10 grams Martian regolith or rock each and the proposal is to return up to 30 sample tubes. The cost will be at least $19.3 MILLION per gram of Martian material returned -- plus the significant risk that the mission will fail or contaminate the samples.

I can't help but wonder is $19.3 MILLION for a gram of Martian dirt reasonable? I suppose Terran scientists can do more elaborate testing here, but is it really worth it? Assuming the sample doesn't contain something astonishing like Martian bacteria or tooth fossil, will the samples really tell us something significantly new or different than what the rovers have tested?

Wouldn't it make more sense for more technology development and cost efficiencies to make sample retrieve more reasonable?