Does the limit of 20 free quotes per language service decrease the business possibilities of LEXIS members who are SYNTAX suppliers?

No, it maximizes them.
Whenever you receive a request for a quote, you know that, in theory, there will always be a minimum 5% probability of your quote being chosen.

So why giving into the weariness of sending dozens of quotes per week if you know that you are competing with hundreds of providers? In the other language services platforms on the Internet, a client does not even have the time to read all the quotes s/he receives.