1) Why should we not have an internal wallet service, where when an individual advertises any crypto for sale, they should be required by the system to have the respective amount within their internal wallet of the respective crypto for the post to be approved for publication. This will help stem out scammers who advertise what they don't have and minimize scam incidences in the forum.
Bitcoin having an open ledger system where wallet amounts are visible to the public could diminish a need for competing wallet services which could be man hour, resource and capital intensive. Many users on this forum have their wallet address listed in their profile and have demonstrated they can move funds from those addresses. It could reduce a need for new wallet platforms to be introduced given how a certain degree of transparency is already built into the system.
2) Why should the system not be updated to ensure that it offers escrow. System escrow can be trusted by everyone. I know individuals offering escrow services may be against this since they earn from it. But think of this, internal escrow creates a sense of security, and everyone involved in the trade will feel safe. The internal escrow can also be used by campaign managers to ensure trust and timely payment.
There are many existing escrow services, some of which could have more capital, better engineers and employees and overall more support.
You have a point in that expansion and one stop shopping are generally good policies to adopt. But I don't know if potential advantages would be cost effective or worthwhile in these cases.