They could. But in countries where internet access is restricted by authorities, running any more than an insignificant amount of traffic over a VPN, even protocols as stealthy as the ones that make them indistinguishable from website (http/s) traffic, can be noticable... and being noticed can get you killed.
Snowflake, on the other hand, runs proxies to users of the snowflake browser extension, who act as entry points. It's named so because connections are ephemeral, and last for a short time, like snowflakes. This makes it much harder to distinguish.
It's not only about what internet traffic, it's also about where.
And of course, the how is relevant too. Not many people want to spend the time to set up an ssl vpn (and multiple people using it makes it easier to spot).
You need to understand what you're asking when you suggest people set up their own proxy. You're asking them to learn a skill, most likely in their free time (free time and energy they may not even have), and without many resources to learn (censored internet), and then rest their lives and livelihoods on that skill. Depending on the regime, maybe the lives of their friends and family, as well.
Comparatively, it's like two clicks to select snowflake as an entrypoint in the tor browser configuration options.