70s, 80s and 90s in English cricket weren't exactly noted for their brilliant organization were they?
But definitely decline of the county game has a lot to with it. Has there been an overseas bowler who's averaged above 50 in england in the given time frame?
Overseas batsmen to average above 50 (min 1000 runs)
Allan Border 2082 @ 65.06
Viv Richards 2057 @ 64.28
Steve Waugh 1633 @ 74.22
Mark Taylor 1584 @ 52.80
Sachin Tendulkar 1575 @ 54.31
Gordon Greenidge 1570 @ 56.07
Shivnarine Chanderpaul 1399 @ 66.61
Rahul Dravid 1376 @ 68.80
Graeme Smith 1355 @ 67.75
Hashim Amla 1086 @ 60.33
(Abbas, Yousuf and Younis all also averaged 50+, with about 800 runs each)
Bowlers who averaged -25 (min 35 wickets)
Shane Warne 129 @ 21.94
Dennis Lillee 96 @ 20.56
Malcolm Marshall 94 @ 18.70
Curtly Ambrose 88 @ 20.77
Glenn McGrath 87 @ 19.34
Courtney Walsh 87 @ 24.44
Terry Alderman 83 @ 19.33
Richard Hadlee 70 @ 24.94
Michael Holding 63 @ 21.12
Joel Garner 55 @ 16.56
Muttiah Muralitharan 48 @ 19.20
Imran Khan 47 @ 24.63
Allan Donald 45 @ 23.62
Andy Roberts 39 @ 20.48
Conclusion: England sucks.