Is there a greater purpose than personal happiness?
No, not really, but...
To find/return/be in the greater happiness --
ah! It's greater because it's more happy, if you like. Better...the way one thing is ok, but another is better. Like that. Say....chocolate ice cream is good, right? Ok, but sex is usually better. Right? But, really great sex is better than just average sex, right? Yes? Ok, now what is the thing that causes the best sex of all? Answer from enough experience: Love. It's the 100% feeling vs the 60% feeling if you like.
Generally people can make an easy mistake: to accept a sorta ok 'good' thing that 'makes them happy', but it turns out not so much. Advertisements can be about getting a person to make that mistake, many ads, such as some auto ads, where an intent is to create a false impression that a certain car will make people like you better, or free your spirit, or make you smile as if you were just 1 year old on a perfect day, or some such falsehood.
It's pretty easy to become more and more lost from what is one's greatest happiness, because those much lesser seeming happinesses take time, energy, investment, and just occupy the space, crowding out.