Because Pakistani Generals are not employee of army chief, they are employee of armed forces of Pakistan. Armed forces work under Army Chief and even though generals may talk ‘for or against’ something within the core commanders’ meeting and lower rank officer may pass their reservations to their immediate army officers, in the end, army chief take decision on behalf of all.
Unless that decision is below moral ground army value (like making decision because of monetary benefit to army chief, taking commission, nepotism, etc), all generals accept that decision regardless of personal reservations, however weak the decision maybe (and obviously, weak or strong decision reflects personality of army chief as well as level of pressure by other generals and circumstances army chief is facing).
But when an army generals in service comes to public for statement, they do not give statement on their own behalf, but they have to give statement on behalf of armed forces of Pakistan and that is, what army chief considered appropriate and decided.
If army general in service makes statement against what army chief decided then obviously that general could get court martialed. … So, generals have two choice when in service … either revolt against their superior (that happens if superior lose moral ground to lead) risking court martial if revolt fails (and that can happen if most in armed forces sides with army chief … as they may not consider chief’s decision below moral ground army value) … or obey orders (though after giving their own opinions to their superiors).
Once retired, an army general speaks for himself, and then they can make statement what they think was right … not what army chief, obviously with consultation of other generals, pressure on him, and due to personal character and value, considered right.
As for timing, Pakistan is not at war … though even war is not excuse for retired army general not to give their opinion in public. What Pakistan and Pakistan armed forces are doing is trying to fight and clear insurgents, traitors, rebels and terrorists who are creating ‘Fitna and Fasad’ within state (Pakistan), and this in no way can be called emergency or state of war situation, rather this is routine matter for many countries.
Actually, what is happening in Pakistan, armed forces fighting terrorists (or rebels, freedom fighters, etc) who are creating fitna and fisad in country, is such that some countries are doing that for years … For instance, Pakistan is fighting such war in Baluchistan since early 1950s (though comparatively at smaller scale), India is fighting such war in Kashmir and other places since 1947. Sri-lanka fought such war with Tamils for decades. Philippines is fighting this war for decades too … and so on.
And whatever General Athar Abbas mentioned, that would not hinder but would help people understand what is happening in the country.
So, calm down. 