I see lots beating about the bush...
First of all, it's not true that Gavasker wasn't picked for WSC & I am quoting from his own Book, "Idols". & it's even more misleading to say that Packer didn't understand Cricket.
What happened is, with ACB officials & ICC, Packer was upset regarding the revenue sharing & timing of the matches. That time WI & PAK were 2 of the best sides with lots of exciting talents, but neither board was Financially strong. Packer decided to launch a parallel Cricket on his own terms (night cricket, time make up - "if an exciting match is hampered by weather, why the F**K we should end in a draw depending on the weather Gods - let's play overtime or let's take the match to extended day, I am sure people 'll not mind....." . Initially, he planned to make 2 teams like 1971 when SAF was barred from touring (AUS Vs. World XI, Gavasker made the World XI along with Engineer, Zaheer & Intekhab). Later Packer got overwhelming support & he could hire entire WI team - so WSC became 3 teams affair - AUS, WI & World XI. They had a series played in WI & probably NZ as well.
Now, Anthony William (aka Tony) Greig was made responsible to hire players for World XVI - he took the ENG, WI & PAK players, Turner & Howarth (?) from NZ, few South Africans as well and contacted 2 Indian players - SM Gavasker & his brother in law GR Vishwanath. Gavasker was in dilemma, but Vishi was in Govt. service (State Bank of IND, I believe) with a great service career in front. We are talking about mid to late 70s, those days Cricketers had to think about the last 30 years of their career, because that time they used to bleed red, instead of blue.... So, Vishi declined considering that it might cost his service career (this is the reason he didn't play in County as well - he used to be in lien with his employer when playing for IND, but they didn't allow him 5 months County window, neither would have given for WSC....) & his brother in law was left alone. At that time, Madhab Mantri (SG's uncle & Vishi's uncle in Law) was an influential BCCI person & he must have his input for those 2. Besides, Col. Hemu Adhikari, a strict Military disciplinarian was Indian Team Manager/Selector (?) & he had his Military style discussion with both these 2 regarding the consequences.........at 27, Gavasker had a great career in front & he was already earning great. I have my reservations on the career stats of SM Gavasker, but in 70s, he was an ultimate run machine - Packer understood cricket more than most & patriotism had nothing to do with Gavasker's declination of WSC.
By the way, those who think that WSC was "not that tough" because Viv & Greg had better career stats in WSC than career are FOOL. People are comparing 20 years career with the best 3 years of Viv Richards & Greg Chappell. No one has any idea what Viv could have done in those 3 years in International, had he played for WI - at 25, he was a 75/75 (average/SR) player in WS "Tests" playing against some of the best ever bowlers. At 28, Greg was the most complete player of his time.
Barry Richards wasn't that great in WSC, neither his 4 Tests career tells what he actually was - but all those bowlers that played against Hampshire in 70s & 80s (In fact all of them that mattered) can tell some of that. Outstanding technician, isolation cost his career, but it cost Cricket more - probably the best ever opening batsman played his Last Test at 24..............