Utah, your question sparked my curiousity so I did a little research, which I don't know if it's definitive. I'm gleaning this from various sources.
"Traditionally" travellers have just never been well incorporated into the educational system. They weren't even allowed to register at many schools (decades ago). That combined with the instability of their lifestyle meant that they weren't well-educated so they didn't have education as a high cultural value (generally, individual variations apply). Education up to 11yo was seen as reasonable (they are adhering to cultural customs of 100 years ago, really).
There are a lot of stories about travellers treated very badly by primary schools just 30-40 years ago, lumped in with all the kids with SN and learning difficulties & left to their own devices, etc. Most modern travellers see the need for their kids to have more years of formal education & qualifications, BUT there's an intra-generational tension, "why should my kids get better educated than me? I did fine.", "Who do they think they are to Lord that over me?" etc.
And as in most cultures, it's the women/females who most preserve the traditions. So if the tradition is not to bother after 11yo...
I was wondering how the Finnish handle educating the Saami (native seasonally nomadic distinct ethnic group). From the bits I've read a lot of similar issues arise (wrt education, anyway).