As a website it's trivial to serve different content to different users. Each page load can or cannot contain a compromised payload. And since the website also

As a website it's trivial to serve different content to different users. Each page load can or cannot contain a compromised payload. And since the website also identifies the users it's also easy to target specific users. To reduce that risk, and temptation, we want to be in a model where the likelihood of detecting a compromised payload is increased. This is why software distributions like Debian are important, because they serve the same content to all their users, and there is a chain of verification that is established. One vigilant user is enough to detect that breach. An even better solution is if the source code is available because it makes it easier for vigilant users to find those undesirable changes. This, paired with reproducible builds also allow to independently verify that the compiled output is indeed produced from that given source code. Somewhere on that line we also have App stores which don't gives much more guarantees than the website but transfer that trust from the publishers to the application distribution platform. A compromised user still has the opportunity to capture the binary and submit it for analysis.