The first major standoff at Depsang happened under Manmohan Singh. And under Modi, Indo-Sino relations were actually pretty good until last year. Even after Doklam, Modi and Xi held two informal meetings.
The rest has already been discussed. In the areas you are referring to, China had been building infrastructure for decades. For example, in Raki Nallah and jeevan Nallah, China had roads leading to its claim line even before 2010. Even if Indian patrols reached certain areas beyond the LAC between those two lines, That area was always dominated by China due to superior infrastructure(until recently) and geographical hallenges. For example, Indian patrols can only go on foot past the bottleneck, and in Pangong, finger 4 acts as a natural barrier and prevents connectivity with the motorable road from Lukung, while China has a road from Sirjiap(well east of finger 8) to foxhole point, on the eastern side of the finger, which is basically a flat beach. The western part is dominated by the ridge. Col. Dinny, who has led patrols there, has explained all of this, but apparently he is a bhakt.
Anyway, this standoff was not just about the areas between the red and pink lines in the map you posted a while back, although China probably did want to further secure its presence in the area. It was about China trying to shift the lac westward to match its historic claim. Otherwise why was China initially demanding India vacate Dhan Singh Thapa as a condition for disengagement, and why did the Chinese Foreign ministry claim the entire Galwan Valley is part of China? The same situation applies in Demchok/Chumar where China claims the entire sector.
And it wasn't just India patrolling China-claimed territory. PLA patrolled well into areas claimed by India. For example Gen. Sharma clearly said that just like India would patrol to its pps, PLA would patrol to the Track Junction and Burtse, well sithin Indian claimed territory. Now both sides are blocking each other at the bottleneck.
