I'm pretty sure Brazil doesn't have a law saying that Google must forbid sideload. I'm sure that government (be it President, Central Bank etc) doesn't pressure Google about it.
I'm sure some private actors (for example, banks) would love that smartphones are as tight as possible (reason: [0]). Perhaps the same reason applies to Google [1]. But no, "Brazil" isn't demanding that from Google.
[0]: consider that some virus (insecure apps, for example) could somehow steal information from bank apps (even as simple as capture login information). The client might sue the bank and the bank might have to prove that their app is secure and the problem was in the client's smartphone.
[1]: the client, the bank etc might complain to Google that their Android is insecure
I'm sure some private actors (for example, banks) would love that smartphones are as tight as possible (reason: [0]). Perhaps the same reason applies to Google [1]. But no, "Brazil" isn't demanding that from Google.
[0]: consider that some virus (insecure apps, for example) could somehow steal information from bank apps (even as simple as capture login information). The client might sue the bank and the bank might have to prove that their app is secure and the problem was in the client's smartphone.
[1]: the client, the bank etc might complain to Google that their Android is insecure