Not all of the carriers require this. eg, Amaysim will sell you an eSIM via their website and will currently sell you 50GB/28days for $10, or 60GB/28 days for $12 (although these deals come and go as you say). You can activate the account and the eSIM via their website, however as has been said previously there are government regulations that will require you to enter ID details, and if you're a foreigner that'll need to be a foreign passport that has been used to pass through immigration (ie, you can't activate until you're already it the country - although I'm pretty sure you can buy the eSIM, you just need it to activate it)