It's damn near impossible to stay in holiday shape all year round, contrary to what Instagram will have you believe. A lot of the more popular "influencers" tend to use a variety of methods to make themselves appear better than they really are. A few examples, camera angles, filters, lighting and a tan make a huge difference. As well as this many people stock pile photos of when they were in shape to post at times when they are not in as good a shape.
For most, if not everyone, it's a lot easier to try and maintain a physique just outside of being holiday ready so it doesn't require a lot of effort to drop a few kilos when needed. For example, I usually sit between about 10-12% body fat and around 85kg. For me this is still pretty lean. To be holiday ready I probably need to be around 8% body fat and about 81 - 82kg depending on how lean I want to get. As I only need to drop a few kilos if I watch my diet and add in a little cardio it won't be too difficult.
What having a near holiday ready body also allows me is more flexibility within my diet and a lot less stress when it comes to getting the fat off. Trying to maintain a perfect physique year round requires more thought about food choices and personally I don't want to have to do that all the time. I'd much rather rather have a little more flexibility throughout the year whilst still being in fairly good shape and be strict when I need to be.
Next time you're looking at someone's Instagram who seems to have enviable abs all year round question whether they have had some help from the examples listed above.