Complex sentence: TECO's then-sophisticated searching operations were motivated by the fact that the offline Flexowriter printouts were not line-numbered; therefore editing locations needed to be specified by context rather than by line number.
Split into simpler sentences: TECO's then-sophisticated searching operations were motivated by the fact that the offline Flexowriter printouts were not line-numbered. Editing locations therefore needed to be specified by context rather than by line number.