In February 2009, Sri Lanka decided to tour Pakistan after India refused to tour them due to the 26/11 attacks on Mumbai. The series was the first Test tour of Pakistan since South Africa visited them in October 2007. Many countries had pulled out in the years before that, citing security reasons. In 2002, New Zealand abandoned their Test series in Pakistan after a suicide bomb attack outside their hotel. With Lashkar-e-Taiba issuing a fatwa against playing Cricket in 2004, calling it against Islam, many teams had been apprehensive about touring Pakistan. On 3rd March, 2009 the bus carrying the Sri Lankan Cricket team to Gaddafi Stadium in Lahore was targeted by militants.
After this attack on the Sri Lankan Team, no country was comfortable in touring Pakistan unless the security situation improved drastically. Pakistan played their home games in Sri Lanka, England and UAE. Eventually, Pakistan made UAE their home away from home.
The security situation in Pakistan hasn't improved much since, and hence teams have not shown interest in playing matches in Pakistan. An International World XI (comprising of retired/out of favour International players, current Afghanistani players etc.) was stitched together and did play 2 T20s in Karachi vs Pakistan All Star XI on consecutive days in October 2012, to assure the international cricket community that situation had improved in Pakistan, and that it was a safe place to play cricket. This did not convince the international cricket community at large. The Pakistan Cricket Board (PCB) tried to get Bangladesh to play in Pakistan. Bangladesh initially agreed, but then backed out citing security concerns.
Finally, this year, the PCB was able to convince Zimbabwe Cricket (ZC) to tour Pakistan for 2 T20Is and 3 ODIs. Reports have suggested that PCB has paid about US $500,000 which includes about US $12,500 to each Zimbabwe player. It is very probable that the cash strapped Zimbabwe Cricket agreed to tour Pakistan because of the money involved. It should also be noted that elaborate security measures were taken: presidential style security was provided to the Zimbabwe cricket team, over 4,000 Security personnel were deployed, the boundary ropes were brought in by a good 30 meters, and all 5 matches were played in the same Gaddafi Stadium in Lahore, en-route to which the Sri Lankan Team was attacked in 2009 and fled in helicopters from inside the stadium.
Cricket fans in Pakistan were overjoyed: the first three matches were incident free and there was a sense of optimism that Cricket had finally returned to Pakistan. The fans were hopeful that more teams would follow in the footsteps of Zimbabwe. But during the fourth game of the tour (2nd ODI) a suicide attack (as per Pakistan’s Federal Information Minister) took place just outside Gaddafi Stadium. The authorities did the right thing by calling it a power transformer blast during the match so that there was no panic amongst the 20,000+ spectators in the ground, but this was a security failure on the part of the authorities. Surprisingly, Zimbabwe agreed to play the 3rd ODI (5th and final match of the tour) after this attack. It is being suggested that they continued to play because of the money which was being offered by the PCB to ZC.
FICA (Federation of International Cricketers' Associations) had warned Zimbabwe against going ahead with this tour, but Zimbabwe went ahead and toured Pakistan. Would other countries be willing to tour Pakistan given the current security situation? Can the PCB continue to offer money to Cricket boards to play in Pakistan? PCB is apparently already in talks with Sri Lanka and Bangladesh to tour Pakistan. I would be very surprised if any other team agrees to tour Pakistan in the near future.
Zimbabwe was a one-off case where a cash-strapped board agreed to send its team despite security concerns. I doubt if any Test Nation will agree to tour unless the security situation as a whole in Pakistan improves drastically.