Scriptures may condemn suicide, because mostly it's done with a purpose.
Anything which is done with a purpose, be it good/bad/ugly -- one has to bear its fruits. If no purpose then no fruits. According to Gita, death has a crucial importance in deciding the next phase, which is based on state of mind. The state of mind is based on what the person has accumulated/learned throughout the life.
BG 8.6 — Also [when] the body is left remembering whatever "Nature" at the end, O son of Kunti, [it] always approaches towards establishing those nature(s) only.
If person is in the state of fear, anxiety, escape, craziness (e.g. "blue whale game"), then those emotions would certainly follow in the afterlife or the next birth. The consciousness either gets trapped for a duration as a ghost or creates a very weak minded person, which is a liability for the society.
Upon committing suicide, a person not only kills a body, but also creates distress for those who are associated with. Hence, "suicide" is condemned.
There are rare scenarios where suicide is not condemned. This is when a person is left with no purpose. A person without any purpose becomes free & realises that the physical body is bound by the 3 modes of Prakruti. Whether one lives or dies.
Note: Tendency to have "no purpose" is also a "purpose". Repenting or being happy with having "no purpose", is also a "purpose". So be careful with the words "no purpose".
e.g. After hearing about the death of Ashwathama, Drona was left with no purpose. His body started showing up those signs. He continued to fight for a while with the enemies, but without purpose. He dropped the weapons, without purpose. He sat in the midst of active battle (unlike Arjuna), without purpose. Went into Kriya yoga and finally didn't find any purpose to breathe. As described in this answer, after leaving the physical body finally his consciousness merged back to Brahman and attained Moksha.
I completely agree that, Whole life is prArabhda. If we are within the scope of prArabhda, where we attach doership, then we have to bear the results of such actions, including suicide.
Outside the scope of prArabhda, one realises that actually there is no doership, it's all fate. Hence sins & virtues don't exist.
BG 5.14 - Neither "Doership" (Kartutva) nor "Actions" (Karma) nor "Reactions" (result of actions) of the people are created by the Omnipotent; But only their nature [3 modes] pervades.
BG 5.15 - The Omnipresent neither accepts anybody's sin nor even virtue. Knowledge remains covered by ignorance. Thus the creatures become deluded.