Actually, it isn't surprising that 10.6 isn't available via internet recovery. That version only exists on DVD, at least AFIK. 10.7 is the earliest version that wasn't available on DVD.

Jon

macOS 11.7.10, iMac Retina 5K 27-inch, late 2014, 3.5 GHz Intel Core i5, 1 TB fusion drive, 16 GB RAM, Epson SureColor P600, Photoshop CC, Lightroom CC, MS Office 365