A "1:1 balun" in this application is usually a common-mode choke. Its function is primarily to reduce common-mode current, rather than to perform any impedance transformation.
Such baluns are easy and inexpensive to fabricate, work on many bands, can handle a lot of power, and have low loss; all because in the differential mode they just look like a length of transmission line.
If there were a trivial way to achieve a 1.5:1 impedance transformation additionally, that would be great. Unfortunately there is not. One could use a transformer with an appropriate turns ratio, but that would involve transferring power through the core with associated loss and other issues. Or an L matching network could be used, but again this comes with loss and other engineering challenges.
In practice, any SWR under 1.6:1 is acceptable for most applications. The SWR losses due to such a mismatch are most likely less than the loss that would be introduced by a matching network.
The SWR loss can be eliminated by using 75 ohm coax. Of course the transmitter will still see a 75 ohm load, but this is within the specifications of most transmitters.