Through diligent by-the-book user thinking that agile coach told you to do, you've concluded that everyone has the problem and your addressable market is the whole industry/world
Disproof
You have specific personas and a description of who’s not your customer
Consequences
You might think you’re designing for a safe average but in reality you’ll be making siloed sub-optimisations for contradictory requirements across multiple target demographics, resulting in an incoherant dumpster fire that nobody will buy. No revenue, no customers, no exit
Should you ever make it to launch, your messaging, distribution, operationalisation and pretty much everything else will be as incoherent, you’ll torch money and die
Causes
Pressure to broaden the scope and 'expand that TAM', buddy
Laziness on the behalf of product and design in particular, or more likely a fear of pushing back
Prior success and the hubris that makes you think that one-to-many is easy because you did zero-to-one
Approaches
The product team needs to drive, not receive, the target market, including calculating viability (with help)
If the pressure is coming from outside the product team, find out what that pressure wants and demonstrate how doing this will not get them it