User blog comment:Bovell/UPDATE: Battlefield 3 demo not yet confirmed/@comment-3062440-20110422181411/@comment-28584497-20110427232754

Pedro, Kelleroid, that is because the companies own their engines.

Pedro, if you want a franchise that changes engines every game, take a look at MoH. EALA never created a proprietary engine/licensed and patented a modified version of an existing engine (like that of IW). Because of that, we've had games running on -- an unspecified engine (MoH & MoHU), id Tech 3 (MoHAA & expansions), console variant of id Tech 3 (MoHF and MoHRS), Lithtech Jupiter (w/ Havok physics), what is probably a Nintendo-made sprite-based engine for Gameboy Advanced (MoHI), an unspecified engine in MoHH and MoHH2 (almost looks like the same engine from the first MoH), UE3 in MoHA, what seems to me to be the console id Tech engine for MoHV, and UE3 again in MoH2010.