why a freelancer is treated badly compared to a team member

I would agree to an extent, but disagree in some regards.

Freelancers/contractors may be used to maintain a stable workforce of direct employees. When additional labor is required, the extra capacity may be filled by contractors so that once the staffing level goes back down, the contractors are let go rather than the direct employees. Part of the justification for the higher wages, is that it comes with less job security.

While I would certainly treat them with the same respect as any other employee on the project, when job cuts are required like many workplaces are experiencing due to the pandemic, they are not treated the same at all. Contractors may be terminated overnight regardless of their importance to a project. It is important for a PM to be cognizant of the fact that organizational staffing strategies may take precedence over individual project needs, and when staffing cuts are required, the PM may have no say in which team members are lost.

A few comments on your response:

1) Freelance contractors are also retained to perform specific tasks that may require skills not available in-house such as scheduling, costing, risk analysis, etc. as well as fill-in positions identified by yourself.

2) Freelancers are typically on contract either through employment firms or personal agreements which dictate fees, employment obligations including hours or work and terminations. Early termination non-compliant with the contract may result in conflict, damage claims and lawsuits.

3) In some jurisdictions freelancers or contract personnel under direct supervision of company staff may be considered "employees" and thus subject to corporate HR policies and employer obligations.

4) The fees paid freelancers can include home office costs, computers and programs to support their specialty, as well as obligatory benefits (in Canada would include CPP, UI, Statutory Holidays, vacation pay, sick leave, etc), plus any administrative costs associated with running a business.

5) One must also recognize that we are in a market driven economy. You have to pay a competitive fee to attract the right professional. This is especially valid when looking to retain specialists.

6) One of the concerns that I have observed in a mixed team of staff and freelancers is the compensation issue. The staff gets to know the freelancer's fee (being significantly greater than staff compensation) and questions set in as to their 'value'. "Why are we paying $150 per hour for Joe whilst my salary works out to $50? We're doing the same job."

7) These concerns and questions should be explored while undertaking the initial Project Risk Analysis - Benefits and Risks of retaining external resources versus in-house staff and/or new hires..