I think they used this evidence against Sidney (the surveillance of them sanitizing the truck and taking things to the burn pile/barrel) because Sidney was the central player. I believe the pros used a very different strategy for Tammy. They inflamed and inflamed her with friends and people testifying as to her anger toward HE. I think their goal was to get TM to testify and try to do what she does best--control the narrative and lie. If I recall correctly, people were worried that the case was not strong enough and, then, Tammy and her sister put the nails in the coffin along with D testimony about the picture that Sidney showed him. TM's team couldn't throw SM under the bus and could not really counteract that testimony.
Excerpt about witnesses against TM:
"The final witness of the day was a former deputy who spoke to Tammy Moorer when the investigation into Elvis' disappearance was underway.
Prosecutors played a video, where Moorer described the relationship between her and her husband as "open".
The investigator said she pulled out a hotel key that she discovered in Elvis' car, and showed it to Moorer.
She said the key led investigators to Sidney Moorer, who had paid for the hotel room.
Lastly, prosecutors made the witness read out a graphic Facebook post allegedly written by Moorer, where she described the affair between her husband and his mistress.
The witness said Moorer used the word "hoe" to describe Elvis, among other words, and placed the blame for the relationship squarely on the 20-year-old."
Tammy Moorer trial day 2: Former family friend testifies against her
Someday when the appeals are done and case can go no further, I hope the prosecution team writes a book or gets interviewed because it will be fascinating to hear the strategies they used for each case.