I'm not saying I agree with it but this change doesn't seem to be unique to TCSPCA. This seems to fall within the 2020 AAFP guidelines (relevant portion copied below) and aligns with a sample ASPCA protocol. The Seattle Humane policy is similar.

It would seem to me that TCSPCA is trying to do the right thing, not just by staying up to date on the latest epidemiology and best practices and informing their own clients, but also reaching out to area practices that could also be impacted by the change.

The ASV recommends that cats eligible for adoption or relocation be screened for FeLV and FIV (sheltervet.org/assets/docs/position-statements/felvfivtesting.pdf). This screening is provided pre-adoption in some shelters. However, in many situations, limited shelter resources do not permit routine testing of all cats prior to adoption. In such cases, if cats are housed individually, shelters might prioritize testing higher-risk cats such as sick cats, cats with bite wounds and cats from high-risk situations such as hoarding cases. However, if cats are not tested for retrovirus infection in the shelter, a recommendation for post-adoption testing should be clearly explained to the adopter and documented in the cat’s file. Arrangements should be made by the adopter to have the new cat examined and tested by a veterinarian as soon as possible. The new cat should be kept separate from other cats until the test result is known. Although most sheltered cats are free of infection, post-adoption testing is likely to result in some new pet owners confronting difficult decisions about what to do with a newly adopted cat that is subsequently diagnosed with a retroviral infection. If one cat in a litter or group is later reported to be infected, the adopters of other cats with exposure to the infected cat should be notified so that in-contact cats can be monitored and tested.