"I also think that the only purpose of metal bats is to make money for coaches and bat companies"
If you think that, you are engaging in conjecture, when the actual facts are readily available to you.
It's sometimes said that we should respect everyone's opinion. I disagree. When facts alone don't answer questions, when you have to apply value systems that may differ from one culture to the next or from one person to the next, then you respect the differences. When an opinion is based purely on bias and willfully ignores factual information to the contrary, it is not worthy of respect.
The intention of those who make metal bats is to meet a demand that existed and continues to exist with or without them, and in so doing, to earn a profit. (This being America and all.) Let's not treat these guys like drug dealers or something. If you want to know why metal bats are made, you have to ask why the buyers wanted them in the first place, and why they continue to want them now.
When I first started in youth baseball in the late 1960's, every Little League team was given a bag full of wood bats that in many cases were years old. Almost all were H&B Louisville Sluggers. They tended to have thicker handles than today's versions. As young pitchers seldom threw very hard back then, they didn't break all that often, so they were around year to year for the most part. But even then, they had to be replaced from time to time.
Some time in the early 1970's, H&B suffered a fire that severely depleted their stock of aging raw timber. (You may not know this, but the bats you buy weren't trees last week. They are aged for years.) When supply is constricted, prices rise so that the supply is effectively rationed. MLB teams got first pick, MiLB teams next, and before you knew it, amateur teams were scrambling to find new sources. I remember a startup company called Hannah ended up supplying most of our youth bats. Turns out they used timber that was not adequately cured, and they broke like balsa wood. Youth programs and others soon found their budgets being busted by the need to (a) pay spiked prices for bats and (b) also replace them much more often.
What followed was a series of attempts to manufacture an artificial bat. Originally, the effort was to replicate the wood bat in shape, weight and weight distribution, and impact on the ball. We had some really clunky early model metal bats. Who here remembers the ill-fated fiberglass bats? They looked like they were carved from soap, and they ultimately were abandoned when it turned out they would shatter if used in cold temperatures. (Yikes!)
Around that same time, Prince racquets were taking over tennis, so it was only natural that, freed from the limits of wood, competition led manufacturers to start engineering their metal bats with alloys designed to enhance their results. They got stronger, whippier, and lighter all at the same time. This is why CWS scores started getting lopsided. That and concerns about player safety have led to repeated rounds of metal bat guidelines, then restrictions.
Metal bats were first made because they were sorely needed. They got more pro-offense because that was where player demand took them. They got more pro-defense when the governing bodies stepped in to restore balance in the game and to bring a safety perspective.
Throughout the entire 40-year period, they have consistently offered a more affordable option to use of wood. They are the proverbial "better mousetrap" in many ways.
As for coaches taking money: This has been going on since Jim Valvano took big-time shoe money and even well before that. Everyone I know would like to have the ability to command high income. Everyone I know would take income willingly offered to them in an honest business transaction. (Some will even be dishonest to do it, but here we are dealing with a common promotional arrangement no different from seeing Justin Timberlake sell us Pepsi.) When people start saying snarky things just because someone else is making money, I think it speaks more to envy than to anything rational.