From the first article you posted a link to:
Although LB is not a particularly new emerging disease, an accurate description of LB epidemiology in Europe is still not possible because few countries have made this disease mandatorily notifiable [3,9,36]. Unfortunately, there appears to be no plan to continuously monitor LB at the European level [37]; instead this is recommended only ‘Where the epidemiological situation in a Member State so warrants ...’, although such situations are not defined [38]. Therefore, surveillance statistics in Europe are based on non-standardised case criteria and uncoordinated systems of data collection [39,40]. Moreover, these data are inaccurate because patients with erythema migrans and other clinically diagnosed cases may be under-reported, the geographical distribution of referrals for testing is unknown, the criteria for serological diagnoses are not standardised, seropositivity due to past infection may be included, and data from remote regions may be lacking [41,42]. In addition, patients may be infected by one or two (rarely three) pathogenic B. burgdorferi genospecies and heterogeneity in symptoms caused by these various agents complicates surveillance.
Apart from testing (which is also affected by the strain of B. Burgdorferi, 'Lyme awareness' is also likely to play a part - in those countries where Lyme in common doctors will be more likely to diagnose it, exaggerating the difference between countries.