For a bit of background:
In 2015 and 2016, Europe became a destination of choice for an estimated 650,000 Syrians. However, this represents only about 5% of all Syrians displaced by the conflict worldwide. Most displaced Syrians continue to live away from their homes within Syria or in Turkey, Jordan and Lebanon. These Europe-bound Syrian refugees crossed the Eastern Mediterranean from Turkey to Greece and applied for asylum in Europe. Most Syrian asylum seekers who arrived in Europe did not stay in Greece but instead continued their journey into Northern and Western Europe after Germany temporarily withdrew from the Dublin Regulation, which requires member states to register asylum seeker applications in the first European country they enter.
It seems to me an obvious answer is in terms of economics (life's not so good in Greece compared to Germany)... but there's also the speed with which Germany processed their applications (cause and effect may be difficult to disentangle on this narrower issue; the so-called "beaten path" effect):
Many Syrians applying in Germany received decisions within three to four months of their initial application, much shorter than many other nationalities. This drove down the average wait times in Europe, since Germany accounted for more than seven-in-ten Syrian application approvals (72%). In many other countries, the wait times for Syrians, as well as asylum seekers of other nationalities, took longer – sometimes a year or more.
Are there some surveys that solicited the asylum seekers' motivation(s) for preferring Germany once they set foot in the EU?