In that case your GM can say 'enemy placement does not allow you to target both'.
Yes GMs can make this call, but his once again leaves the work onto the GMs which results in inconstant experiences for players especially in SRM play.
Yes, Multiple Attacks leaves this up to the GM. And given how there's no formalized 'how close can they be for attack style X to be capable of hitting multiple enemies', it's either GM-leeway, unbelievable 180-degree scenarios, or completely banning it from SRM.
It doesn't say that you only pull the trigger once. It says that you "pumps out multiple rounds with a single trigger pull"
If they wanted a wide burst to be a double burst, they'd have called it a double burst or explicitly have called out that you still pulled the trigger twice. They didn't. Yet they mentioned double-pulling in the SA mode. So it sounds extremely unlikely to me that the wide burst is 2 trigger pulls. Your interpretation goes directly against the language used here. As such, I find your interpretation to make far less sense in all accounts, and your 180-degree scenario extremely unrealistic as supposedly intended. The only way a 'it might be a double-pull' argument could have made any sense, was if SA hadn't explicitly mentioned a double-pull.
And if we're going to go back to SR5 again: SR5 explicitly noted a Long Burst was pulling the trigger twice in BF-mode. So a Burst, whether narrow or wide, was 1 pull. And the explicit double-pull is not mentioned in BF, but is mentioned in SA. So even if we compare SR5 language to SR6, SR6 language is different enough to eliminate any double-pull arguments.
If you want to attack 2 people that cannot possibly be covered by 1 attack: Use dualwielding. Don't go down the road of 'hey the rules may say X, but they don't say Y, so obviously !Y is perfectly fine'. The rules also don't say that you can't hit 30 people with 10 rounds, but that doesn't mean I can.