The phrase "were subject to" implies being under the influence or control of someone or something. There are many synonyms for this phrase, including "were susceptible to," "were prone to," "were vulnerable to," "were at risk of," and "were exposed to." These alternatives can be used interchangeably with "were subject to" to convey a similar meaning in various contexts. For example, one might say, "The company's profits were subject to market fluctuations," or "The building was vulnerable to earthquake damage." In both cases, the phrases "were susceptible to" or "were at risk of" could be used instead.