This is the 3177th most frequent Japanese word.
取り残さ
"取り残さ" means "to leave behind" or "to be left behind."
In this sentence, '取り残さ' (in its conjugated form '取り残されてしまいました') is used to express the action of being left behind or excluded by others.
彼はみんなに取り残されてしまいました。
He was left behind by everyone.
Here, '取り残さ' (conjugated as '取り残された') refers to objects that were forgotten or left unattended.
取り残された荷物が駅にはまだ置いてありました。
The luggage that was left behind was still at the station.
In this usage, '取り残さ' describes concepts or objects that were not carried forward or adopted into modern practices.