The case of Spain is not highly representative since B types visas are ordered in extraordinary circumstances. Spanish people is allowed to enter USA by having an eVisa: https://en.wikipedia.org/wiki/Electronic_System_for_Travel_A... About your exact question I do not know why that difference in 2011 and the following years. It would be interesting to know.
I only found that in 2011 the ESTA fee was introduced but I do not know if there were more changes in the visa policy.
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The case of Spain is not highly representative since B types visas are ordered in extraordinary circumstances. Spanish people is allowed to enter USA by having an eVisa: https://en.wikipedia.org/wiki/Electronic_System_for_Travel_A... About your exact question I do not know why that difference in 2011 and the following years. It would be interesting to know.
I only found that in 2011 the ESTA fee was introduced but I do not know if there were more changes in the visa policy.