If there are two stand-alone phrases in a sentence, use a comma (or a semi-colon): Comma Splices When you want to join two independent clauses, you need a conjunction or a semicolon. A comma alone isn’t strong enough to join them. This kind of mistake is called a comma splice. Incorrect: We were out of milk, I went to the store. You can fix a comma splice by adding a conjunction or changing the comma to a semicolon. Correct: We were out of milk, so I went to the store. Correct: We were out of milk; I went to the store. Source: https://www.grammarly.com/blog/comma/

Mira, las comas no se ocupan muy muy seguido... Se podría utilizar más para dar un en listado Por ejemplo: A mi me gusta correr, chatear, caminar, gritar, etc. U otro ejemplo sería en Aposición. - La mañana, mientras tanto, comenzaba a aparecer con la salida brillante del sol. O por ejemplo en Secuencia de hechos.... -Armaron los bolsos, abrieron la puerta, y antes de darse cuenta ya estaban en el viaje. .

I think the second example should use a comma for the same reason that the first one uses it. It shows that you're reordered the clauses in the sentence. "As" is being used like "because" and starts a dependent clause. You show that you moved the primary or independent clause / idea to the end by putting a comma between the two clauses. In short, commas are used whenever you combine or reorder simple ideas so that you can see what the main ideas are.

Comma placement in complex sentences can be quite confusing and is a common mistake with native English users as well (myself included if the corrections on my reports are anything to go by). I think in this case your first sentence has the dependant clause first which is why it requires the comma. It could be written as "My parents went on a food tour because they like food" (no comma). Where the dependent clause is now last. The original uses "as" as an independent marker, as you pointed out. It could also be written as two separate sentences "My parents enjoy traditional food. My parents went on a food tour". I think that the second sentence would not make any sense if you broke it up. "It was a really good experience" - what was a good experience? So it is a single clause. At least I think that's why. There's some good information here about this stuff if you want to have a look: https://owl.purdue.edu/owl/general_writing/punctuation/independent_and_dependent_clauses/index.html But don't panic about this, unless you need it for an exam or something. Most of the time it won't change the meaning of your sentence. Or you would be understood anyway.