It's hard to overstate just how much LE changed things. They made TLS the default, so much that you didn't have to keep unencrypted HTTP around any more. Kudos.
Snowden's revelations were a convincing argument, but I would place more weight on Google in its "we are become Evil" phase (realistically, ever since they attained escape velocity to megacorphood and search monopoly status), who strove to amass all that juicy user data and not let the ISPs or whoever else have a peek, retaining exclusivity. A competition-thwarting move with nice side benefits, that is. That's not to say that ISPs would've known to use that data effectively, but somebody might, and why not eliminate a potential threat systemically if possible?
Snowden may have been a coincidence, too. We knew encryption was better, it was just too much of a hassle for most sites.
The problem is that there are active bad guys. Redirection means when there are no bad guys or only passive bad guys, the traffic is encrypted, but bad guys just ensure the redirect sends people to their site instead.
Users who go to http://mysite.example/ would be "redirected" to https://mysite.example/ but that redirection wasn't protected so instead the active bad guy ensures they're redirected to https://scam.example/mysite/ and look, it has the padlock symbol and it says mysite in the bar, what more do you want?
Snowden was definitely a coincidence in the sense that this wasn't a pull decision. Users didn't demand this as a result of Snowden. However, Snowden is why BCP #188 (RFC 7258) aka "Pervasive Monitoring is an Attack" happened, and certainly BCP #188 helped because it was shorthand for why the arguments against encryption everywhere were bogus. One or another advocate for some group who supposedly "need" to be able to snoop on you stands up, gives a twenty minute presentation about why although they think encryption is great, they do need to er, not have encryption, the response in one sentence is "BCP 188 says don't do this". Case closed, go away.
There are always people who insist they have a legitimate need to snoop. Right now in Europe they're pulling on people's "protect the children" heart strings, but we already know - also in Europe that the very moment they get a tiny crack for this narrative in march giant corporations who demand they must snoop to ensure they get their money, and government espionage need to snoop on everybody to ensure they don't get out of line.
You can do better than this. You can have your mitm proxy follow the SSL redirect itself, but still present plain HTTP to the client. So the client still sees the true "mysite.example" domain in the URL bar (albeit on plain http), and the server has a good SSL session, but the attacker gets to see all of the traffic.
(I do work at Mozilla now, but this predates me. Still think it's one of its most significant (and sadly often overlooked) contributions though.)
LE allowed more sites to get certificates. This has obvious benefits for e-commerce, for example
But so-called "tech" companies, e.g., "Big Tech", have, since before and after LE was started, continued to perform the largest mass scale intentional erosion of privacy in human history
The exfiltrated data is encrypted in transit using TLS. This may prevent ISPs or other passive network observers from competing with the so-called "tech" companies in the data collection, surveillance and ad services business
Arguably the use of TLS certificates increases privacy from ISPs or other passive network observers, but it does not increase privacy from so-called "tech" companies, who are perhaps the greatest threat to privacy that computer users face. Their "business model" depends on violating privacy norms
And, in fact, commercial CA certificates as pre-installed in browsers and required on the www ("WebPKI") effectively obstructs computer users from monitoring their own egress traffic in real-time. Hence corporations and other computer users must work around "WebPKI" to perform "TLS inspection"
M