That's a GREAT question. Information Technology is $5.6T market, and telecommunications services is another $1.8T [1]. Uber and AirBnB, which I believe ARE tech companies, are under $90B combined, so ~2% of IT sector.

SpaceX is aerospace: ~$12B valuation vs ~$600B Aerospace & Defense industry size, and Tesla is automotive, $28B vs ~$750B Auto + components market.

Note that Uber, AirBnB, SpaceX and Tesla are probably the biggest unicorns out there.

But you are raising an important point - many industries will be redefined when new competitors are using IT much more heavily. Still, that growth mostly comes from existing players, and I believe the growth of the IT sector itself is limited now.

[1] https://eresearch.fidelity.com/eresearch/markets_sectors/sec...

edit: typos, minor clarifications.