Organic posting on LinkedIn, Facebook and Instagram has no manner to target the right audience, but only your followers, which at the time of the post might not be interested in the offered service or product. In addition, organic posting on Lin, Fb and IG has always very low reach, and therefore very low engagement and very low conversion. This is made this way by those platforms algorithms on purpose so users buy Ads instead.
Reach in organic posting is between 0.01 % and 0.1 % at the most. So, very low reach and no targeting the right audience means that organic posting is not recommended for sales but only for branding and trust. For sales it is recommended Ads in those platforms targeting the right audience by using those platforms big databases targeting variables. Reach in Ads is also low, probably between 0.01% and 5%, but paid audience is much larger than organic audience, therefore absolute reach is higher, plus with a right target audience in Ads, the engagement and conversion rates should be higher too.