I also don't understand how they can eat Manjar sandwiches but not Peanut Butter and jelly...
Do you mean why can't you buy PB&J sandwiches in the shops/cafes? If so, I've never seen them sold in any shop anywhere I've travelled in the world (I've never been to the USA, so maybe it's exclusively a USA thing?), but most people I know are capable of taking a slice of bread, adding PB&J and eating it.
I've also never seen a manjar sandwich sold in a shop, so I'm assuming you mean why can't they *make* it, or perhaps, why don't they *like* it. Which could simply be due to personal taste. Just like if you're from the USA, you probably won't like vegemite or marmite and again, even in Australia, vegemite sandwiches are usually not on the menu at cafes.
As for store/cafe bought, the choices are varied. Churrasco Completos or Ham/Turkey, Cheese & Avo, Barros Luco etc.
If you are craving a particular sandwich, nothing stops you from *gasp* making it. You can buy pretty much any ingredient that you like, there are at least 30 varieties of bread in the supermarket, from Ciabatta, to heavy German seed bread, light wholewheat, maraquetas, allullas, raising bread etc. There are many different types of ham (honey baked, smoked, turkey, chicken etc) and you are allowed to add more than one slice if you must. For a bit of excitement, you may even add any of the range of about 20 mustards available, mayonnaise, sour kraut, pickles or any other topping you desire.
So, I think it's safe to say that sandwiches can be good in Chile. (Just quietly, I also don't think that PB&J should be held as the bar to which good sandwiches are judged)
PS
'Tis I buying all the Peanut butter, there will be riot in this house if we ever run out!