You only have to see the amount of texts that are published in Steemit when the SBD was worth more than $ 10 and the amount of texts that are written now, to give you the reason. Almost everything in society is a game of incentives, if you are rewarded for doing something once, you will want a reward every time you do it. Therefore, when lowering the value of SBD, many people became discouraged and lowered their production of texts, since the reward for publishing had also fallen.
Of course, this does not apply to all people, because there are people who have other incentives that are not money income, however, the rule continues to apply, instead of money the reward for these people can be anything else.
Yup, it shows when the price drops, ppl drop from the platform like flies too :P