#4 A filler feud between Royal Rumble and WrestleMania

As you're probably aware, Seth Rollins is the favourite to win the 2019 Royal Rumble. What usually happens after a superstar wins the Royal Rumble is that they have to wait it out for another month until beginning their WrestleMania rivalry with the targetted champion.
With two PPVs set between Rumble and WrestleMania, there's undoubtedly going to be some filler, and Rollins vs Lashley could very well be the program. WHY there are two PPVs between the two big shows is a mystery. Feels like oversaturation.
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#3 To protect Seth Rollins

Seth Rollins was on the verge of beating Dean Ambrose clean until Bobby Lashley came out and played the spoils. The most likely reason for Lashley assaulting Rollins was so WWE could protect The Architect.
After all, it wouldn't look too good if he lost clean to Ambrose. This only further cements the big babyface push that's about to come for him.