To add a little more nuance, what you say is true for most people. I'm a bit of an exception to this, but there's a catch.

Personally, I can have abs all year round and maintain this kind of ripped physique in a healthy state. But there's a huge catch, I'm a natural ectomorph. I have thin wrists, thin arms and a small frame. Being at a low body-fat is my natural baseline; putting on weight is near-impossible. I could eat Mcdonalds all day and basically look the same. People are often jealous of this but they shouldn't be, being natural ectomorph comes with it's own challenges.

I could take a zoomed-in photo of myself, put it on Instagram and fool people into thinking I had a God-like body. But zoom out and you'll see I have a skinny frame that looks less impressive.

The vast majority of people are mesomorphs or endomorphs, and maintaining "Instagram abs" is going to be a constant and unhealthy struggle, like you say.

Also, as I'm sure you're aware there are all kinds of tricks to fooling your Instagram audience into thinking your body is far more impressive than it really is: lighting, poses, post-workout pumped muscles. On top of that, there's the increasing steroid-use. Nothing on social media can be taken at face value.