The books adjust spreads inorder to get as close to a 50-50 split on money bet on the 2 opponents.

A Books business model is to make the lions share of their profit on the "Vig" ( vigorish). That (-110) part of the point spread. Often they use the vig as enticement to get money placed on one side or the other.

A big (+) amount one one side of a toss up vs a bigger (-) amount on the other side is an adjustment to where the betting public has there money.

Team x -1 (+130) vs team y +1(-175) means the book believes it's a tossup game. But the betting public has laid its cash at at least 65% on team y. The vigorish adjusts according to what it takes to get an even payout no matter who wins.

The vig creates a break even point for the bookie. The vig is then adjusted up or down to create the sweet spot, where no matter the outcome. The books wins a profit. Hence the reason negative vig is always much higher than positive Vig.

The "sharps" ( professional gamblers), they watch the Vig closer than the spread. On key matchups, with large swings in vig. The sharps will " middle" the spread. Trying to beat the book at their own game. Betting on both sides & guaranteeing the sharp gets a profit no matter the outcome. For this reason. The closer to game time. The books often witness large. Very large chunks of money getting placed right before the lines lock. Like a roulette wheel croupier saying, " No more bets".

In our modern era. Both sides. The book & the sharp are employing algorithms to identify middling opportunities.

This is a trillion dollar industry.
I'm surprised there isn't somebody out there selling algorithm software to the betting public.