Our tax system often encourages “doing it yourself” (DIY), because when you buy products or services from others, you pay sales taxes and they pay income taxes, none of which you pay if you just do it yourself. But I see larger forces encouraging DIY.
Matchmaking seems prone to adverse selection (as does the normal dating market); the people who most need extra help are the ones who suck, so people who don't suck will refuse to meet with people who hire a matchmaker.
If you lived in a dorm, the professional would decorate your home at the same time that they decorated hundreds of others, by doing them all similarly. That way is vastly cheaper.
Re: DIY. I'm personally happy to let a "professional" decorate my home but it just costs way too much to do so. I'm happy to use professionally designed furniture from IKEA though because its affordable and I'm even open to designing my rooms after IKEAs designs because their advice is free of charge. Same with things like basic plumbing/electrical work - its cheaper to buy the most expensive professional tools on the market (and literally donate them to charity the next day if you're so inclined) than hire a professional. No thanks, DIY it is.
Re: matchmaking. The real reason is that people want to maximize the quality of their match, not just the "success" of it. I.e. someone who's a 5/10 could reasonably find a 5/10 partner and get married, its not *that* hard for most people. But what they really hope for is a 6/10 partner or even a 7/10 if they can really shoot for the stars (which happens in real life, just very very unlikely). Yet a matchmaker is only likely to offer you a 5/10 match as they want to balance the needs of both sides.
Services that do offer you a better looking partner (i.e. "mail order brides") used to be somewhat successful but were overshadowed by the ease of using the Internet instead.
It can also be very very easily faked, especially these days.
"If I had a humble spirit in my service who, when I asked for a glass of water, brought me the world's costliest wines blended in a chalice, I should dismiss him, in order to teach him that my pleasure consists, not in what I enjoy, but in having my own way.” - Søren Kierkegaard
To point out the obvious (one of my skills), couples would have an incentive the quit marginal relationships early to avoid the $X/month fee - if I have a lousy relationship with my spouse at $X/month, I can probably have a no-worse one with somebody else for free.
More broadly, traditional old-fashioned matchmakers did mostly work by word-of-mouth (to parents, mediated by gossip, local religious and civic leaders, etc.).
Perhaps those matchmakers went out of fashion because of the general increase in independence of young people - parents don't much control mating of their kids anymore.
If not that, why would be interesting to know.
The difference is that performance here is much noisier than in most trades, and so much harder to judge. Word of mouth seems insufficient to judge quality.
Or... maybe wanna-be matchmakers could simply offer their services for free (or nearly free) for a couple of years, then gradually collect positive reviews/testimonials from people they were able to match up and who thought highly enough of them to express their opinions to others. Once a new matchmaker established such a modest reputation for success, he/she could start to charge for his/her services. And once there were a lot of matchmakers, new wannabes could work as apprentices to the established ones, thus learning the trade, building their own reputations, etc. Is this not how people generally became successful tradesmen in the past?