I also use google flights but I thought google flights was created after Google acquired ITA software. Isn't it ITA's backend behind google.com/flights?
Yes.
Google Flights is simply a pretty UI around matrix.itasoftware.com, no?
The matrix has nice features like flexible dates on a multi-leg trip that Google Flights doesn't offer.
Google Flights has gradually added ITA Matrix stuff over time.
You can nerd out a lot more with Ita about specific routing and airlines