There are definitely reasons not to change jobs constantly. It kind of depends on industry.
Finding a new job might mean you need to relocate, which is inconvenient and becomes harder if you own a home or have a family.
There is also always a risk that the new company’s culture or your new boss are bad. It’s not something you can really know for sure until you switch, but if they aren’t good, it might not be worth the extra money.
It also takes time to ramp up and figure out the way things work. Being new in a job kinda sucks for a lot of reasons.
Your current job might offer something that is hard to find elsewhere like flexibility to work remotely when you want, or free food, or a good 401k match.
Some benefits take time to accrue and starting over at a new company might mean starting over on benefits accrual. For example, some companies increase vacation days based on years of service. Same goes for other things like percentage of 401k match. You might also miss out on claiming the full 401k match that you’ve earned at your current job if you leave early depending on vesting schedules.
Some companies have better job security than others. A new company might pay more, but also do regular layoffs. If your current company is fairly stable, it might not be worth it to move to one that does more layoffs.
Your current employer might pay close to top of market already. It could be hard to find another employer that actually would pay you more, and even if they could, it might not be worth the little extra for all of the other above cited risks of changing jobs.