Historical context plays a part on both counts.
In terms of the Polish psyche, for the last several centuries, their country simply didn't exist, partitioned by neighbouring powers. When a Polish nation was finally reformed after WW1, it didn't have long before it was overrun by the Nazis, and then overrun by the Soviets, who didn't exactly provide the best standard of living. Poles have, quite simply, put up with a
lot of crap as a people and make the best of it, so even the troubles they receive in the UK can be rather light in comparison, especially given the financial benefits of being here.
With regards to why they get more flak, the most obvious factors are their higher visibility and the ability of the UK population to recognise signs of being Polish (or at least slavic, but people will presume Polish), which in turn comes from how the Polish are somewhat more well established than other migrant communities because of... well, WW2. During the war a lot of Polish military personnel fled to the UK in order to continue the fight while their country was occupied, and it was also where a lot of prisoners would be sent when the Allies liberated their camps - like my grandfather. Many of those people grew to like the UK as it had it become their second home, especially as an alternative to a homeland under Soviet rule, and so stayed here. Thus when the cold war finally ended and Poland quite eagerly joined the EU, the UK was well primed as a location for new Polish migrants to travel to. While folks like my Dad love the fact he can now easily find a Polish shop when he wants some kielbasa, to others its a clear signal that there is a sizeable population of Polish immigrants living in the area, and they begin to adjust their sights.
I mean to put it another way,
Poles in the United Kingdom is its own wikipedia article.