Learn Spanish (Latin America): El rodillo se atascó por no lubricar el engranaje. - The roller got jammed for not lubricating the gear.

There is no specific subject! Similar to the impersonal instructions you are learning (like no fumar), Spanish often uses the infinitive for general, unspecified actions. Here, por no lubricar implies that the gear was not lubricated by anyone in particular. English would often use the passive voice here ("because the gear wasn't lubricated").

Why use por instead of porque to say "because"?

Porque must be followed by a conjugated verb (like porque no lubricaron). When you want to say "because of" or "due to" followed by an action in its infinitive form, you must use the preposition por.

Why is it se atascó instead of just atascó?

The base verb atascar means to jam or block something else. By adding the pronoun se, you create the pronominal verb atascarse, which means "to get stuck" or "to become jammed". This is how Spanish expresses that a change of state happened to the roller.

Could I use se rompió instead of se atascó here?

They have different meanings. Romperse means to break entirely, whereas atascarse specifically means to get physically stuck, jammed, or clogged. It is the perfect vocabulary word for mechanical parts that stop moving but are not necessarily broken.