Companies hold assets, cash flow and perform real world activities that have a tangible value. There are multiple ways that value can be realised. Aside from speculative investors which were discussing, companies and individuals can buy shares in order to exert strategic influence over the company for their own reasons, so the shares have a value to them beyond just the share price. For example the way Microsoft owned shares in Apple for a long time because the existence and operations of Apple at the time benefited them. Ultimately management can buy out the company, or an external player can mount a takeover, or there could be a merger, any of which can lead to a cash out situation.

E.g. a software company might never pay a dividend, but the company might be bought by a company that wants to acquire it's products or customers, or it's technology team. These things have economic value that can be realised. So there are multiple ways a company can have value that can lead to share owners benefiting from the materialisation of that value.