Huh? Are you comparing FM3085 or ER3145 to FM3145? Since 3100 there were 3 different Caesers . . . and when the caeser changes, then policy can change- sometimes drastically.
You are also changing topics- you think a campaign does not make sense but you have much more OOC information than the policy makers have IC, and thus some things might not make sense because you have that complete picture.
The Marian Hegemony has spent the years since the Blackout in a relative state of quiet. With their military spent from years of fighting in the Lothian territories, they are in no position to take advantage of the lack of communications with aggressive action against their neighbors.
Era Report 3145, page 76
This announcement is indicative of the type of Caesar that Ignatius has been since he came to power. Given to impulsive decisions and rash judgments, he can be capriciously cruel at the worst of times. Yet there is another side to him, one that composes humorous poetry for sick children, or dedicates a botanical garden on Alphard for the free use of the public.
Era Report 3145, page 113
Still, Caesar Ignatius has refrained from territorial expansion and has instead concentrated on intense raiding across the long Periphery border with the Free Worlds League and deep into the Magistracy of Canopus—activities that seem aimed more at projecting and honing the MHAF’s strength.
Field Manual 3145, page 185
Unlike his father or grandfather, Ignatius supports diplomatic and cultural ties with nearby unaffiliated worlds....This has enabled the Hegemony’s sphere of influence to extend itself with far less bloodshed throughout the 3140s.
Field Manual 3145, page 185
This recovery has been slowed by increased combat action across the coreward region of the Hegemony, where the I, II, and III Legios have all been experiencing nearly triple the number of bandit raids since hostilities with the Lothian League were suspended.
Field Manual 3145, page 196
From this sources, we can find that the MH spend most of their post Jihad years rebuilding their nation and armed forces, and dealing (badly) with the Lothians. After 2 dead Cesars, Ignatius just said "screw that" i forgot about Lothario. Now, we can see the MHAF rebuilding and improving their officer corps with some limited raiding, while diplomatically trying a "soft power" approach with the independants like Niops and New St. Andrews, with military selling and spots in their military academies. We also see, from other sources, that the MH supported pirate bands to attack the MoC and the various ex-FWL states to have them busy.
I have to concede that Ignatius is mercurial, the guy guy have a bad case of Bipolarism, but he is mostly a politician and diplomat before a warrior, and i can see the MHAF command advicing against dealing with a reformed FWL.
Then, in Shattered Fortress you have the MH heavily raiding Tamarind, invading 2 planets in the Rim Commonality for no apparent reason, and a former canopian planet. This were not raids, or crash and grab actions, these were full blown invasions, and after some action, retreats. And then Tamarind get mechs and mercs from who know where (after the heavy losses the Tamarid Regular had for the previous years) and began to invade the MH.
So, either Ignatius got full tin-pot dictator, fell to a "clever capellan trick" (see Shattered Fortress page 37), took "stupid pills", have IC information that forced him to order those actions, all of the above, or maybe some other reason we don't know.