Are there any advantages in embedding them into the app? Why can't I have them published on my website?
You can have them on your website, is your choice, but you have to consider a few things.
Cons having popups in your app, they might not always work, tos policy needs to be on a 24/7 website hosted which not always happens from various reasons, the business isn't generating enough to pay for the hosting etc.
Another con would be each new android/ios/browser/update popups are handled differently, in past as if i recall correctly some android games didn't had popups or redirects to other games properly working.
Now the above are not very serious cons but they matter to a more "picky user".
There are a few advantages like:
Your app looks a bit more professional and you get a bit more trust from people as you appear to care of your business.
You don't have to worry about the policy /tos being hosted = no hosting costs.
Avoiding popup blockers and other issues regarding iapp redirects.
Now all of them are not very bad things or good things, but it probably takes 5 minutes to add them and they don't do any harm to no one.
As if you'll ask what if i want to update my policy, you can have a free hosting service and fetch the policy and tos from there. Same applies for the above "0 costs hosting". But when you have a freehosting service, they might not always have SSL and some browsers might give users warnings as "not secure", making your app look suspicious.
And finally chances are nobody will actually read your policy or tos agreement, but if someone decides to sue you because while playing your game they got annoyed and smashed their device, and they have access 24/7 to your privacy and tos without any interference from your hosting provider etc... then you are covered, and they wont be able to claim a brand new iphone plus damages of not being in contact with their friends/business because of your game. As well in the case of a data leech, you will be covered much easier as your tos would probably have something along the lines if you dont agree with this TOS then uninstall the app and be in the users ability to read whenever they want 24/7.
Nobody is going to force you to have them built in ... is just that old saying ... "the little things make the difference" and the other golden saying "better safe then sorry".
There are probably more advantages and cons, but this are the few that pop'd in my head now as a simple logic.
Sorry if i smashed some words or sentences into a potato pulp.