All of my UA flights over the last year have been uneventful (on time, no missed connections, etc....) and for the most part I always received the surveys. My last three UA flights (ORD-FRA and KWI-IAD-ORD) over the last two weeks were also uneventful and I didnt receive the survey for any of them (though I did receive a Star Alliance survey for the ORD-FRA flight). So is it malicious or just by happenstance, who knows?