1) Element or other matrix components do not require a copy right transfer. That means Element is hard to re-license under another license than its current one.
2) The license for Element is Apache 2.0. A fine choice for any OSS project looking to maintain a healthy ecosystem of contributors for decades to come.
3) The ecosystem has a diversity of stakeholders and contributors outside of Element the company maintaining various components, integrations, etc. It's an ecosystem that already serves many millions of users.
4) Not all the Matrix components are under the Element umbrella (see 3). Element is probably dominant in this community but it's based on merit rather than ownership. E.g. the Matrix foundation is mostly run by people outside of Element. Even the Element apps have contributions from outside Element the company (see 1).
5) Decentralization is at the core of the Element sales pitch. They are unlikely to want to walk back on that; or even be able to do that without damaging their credibility. For better or worse, that's what they are selling and stuck with. And they seem successful with it too. Hence the investment.