There are a number of ways that a VC who owns less that 50% of the company can still push through changes like this.

In some cases this will flat out be a condition of investment, so it is agreed on in advance. If you are really anxious to close the deal it is easy to see why you might agree.

In other cases the composition of the board might be such that a majority might vote for a CEO change. This can be the case when, in addition to the founders and the VCs on the board, there are "independent" directors who might vote with the VCs. If the independents+VCs is greater than 50% of the board, they can usually make a change of CEO.

If the VC does not have 50%, but no individual founder does either, it is possible for the VCs to convince some of the non-CEO founders that it would make sense to bring on "professional" management to increase the possibility of success. Particularly if the founders have some disagreements, this can be tempting.

One other thing that can happen is that as a company goes out to pursue additional rounds of financing, the existing VCs can use that process as leverage to force a change. For example, if they say that they won't invest their pro-rata share in a new round, that can often be a warning sign to other investors. So, the VC might threaten to withhold that investment to convince the CEO to step down.

Majority ownership means a lot, but it is not everything.

Oh yes it can! It is called the Investor Agreement. A 10% shareholder or less can control the company if the terms are in the agreement. Most agreements are not publicly available so it is difficult to know what is going on when you compare deals. Have you ever made an angel investment and then regreted that you did not have more control? VCs have. It is like who wins in the end, it all depends on the x of the VC investment. It is not what it says on the can, it is what's inside that matters.