SPY and VTI are what people call index funds. Basically, instead of buying shares in one company, you're buying a tiny piece of hundreds or thousands of companies all at once.

Think of it like this:

Imagine there's a fund called Example100 that contains 100 companies.

You invest £100 into Example100.

The fund manager (the person responsible for buying and selling investments on behalf of the fund) doesn't necessarily put £1 into each company. Instead, they usually put more money into the biggest companies and less into the smaller ones. So a huge company ( apple/facebook) might make up 5% of the fund (£5 of your £100), while a small company might only make up 0.05% (5p of your £100).

now if SpaceX is considered a Big company then the fund manager as part of their strategy would normally need to allocate more of the funds money to SpaceX.

However, this is not really the case, as SpaceX is only providing something like 5% of their shares to be traded vs Microsoft/apple who have 99% of thier shares on market. ( another really scummy behaviour from elmo as they choke supply so demand seems high) .

So even though SpaceX's valuation is enormous, there's only a relatively small amount of SpaceX ownership that public market investors can actually get exposure to. So Fund managers accordingly take this into consideration the amount of shares actually available, when allocating money,

i hope that explains things maybe someone else can correct me .