When `BPF(eBPF)` traces the call stack, all user-mode functions are `[unknown]`. Why is this?

Experimental environment

┌──[root@vms99.liruilongs.github.io]-[/usr/share/bcc/tools]
└─$hostnamectl
   Static hostname: vms99.liruilongs.github.io
         Icon name: computer-vm
           Chassis: vm
        Machine ID: ea70bf6266cb413c84266d4153276342
           Boot ID: 0d01838b0095494c82d1befb174a317d
    Virtualization: vmware
  Operating System: Rocky Linux 8.9 (Green Obsidian)
       CPE OS Name: cpe:/o:rocky:rocky:8:GA
            Kernel: Linux 4.18.0-513.9.1.el8_9.x86_64
      Architecture: x86-64
┌──[root@vms99.liruilongs.github.io]-[/usr/share/bcc/tools]
└─$

When using BPF/eBPF to trace the call stack, I found that all user-mode functions are [unknown]

┌──[root@vms99.liruilongs.github.io]-[/usr/share/bcc/tools]
└─$profile
Sampling at 49 Hertz of all threads by user + kernel stack... Hit Ctrl-C to end.
^C
    _raw_spin_unlock_irqrestore
    _raw_spin_unlock_irqrestore
    prepare_to_swait_event
    rcu_gp_kthread
    kthread
    ret_from_fork
    -                rcu_sched (14)
        1

    kmem_cache_alloc_node
    kmem_cache_alloc_node
    __alloc_skb
    __ip_append_data.isra.50
    ip_append_data.part.51
    ip_send_unicast_reply
    tcp_v4_send_reset
    tcp_v4_rcv
    ip_protocol_deliver_rcu
    ip_local_deliver_finish
    ip_local_deliver
    ip_rcv
    __netif_receive_skb_core
    process_backlog
    __napi_poll
    net_rx_action
    __softirqentry_text_start
    do_softirq_own_stack
    do_softirq.part.16
    __local_bh_enable_ip
    ip_finish_output2
    ip_output
    __ip_queue_xmit
    __tcp_transmit_skb
    tcp_connect
    tcp_v4_connect
    __inet_stream_connect
    inet_stream_connect
    __sys_connect
    __x64_sys_connect
    do_syscall_64
    entry_SYSCALL_64_after_hwframe
    [unknown]
    -                haproxy (1203)
        1

    show_vma_header_prefix
    show_vma_header_prefix
    show_map_vma
    show_map
    seq_read
    vfs_read
    ksys_read
    do_syscall_64
    entry_SYSCALL_64_after_hwframe
    [unknown]
    [unknown]
    -                awk (39726)
        1
.............        
┌──[root@vms99.liruilongs.github.io]-[/usr/share/bcc/tools]
└─$

What is the reason for this? Is it because the program lacks debugging information? Or some other reason? I used Python to write a lock demo, and this also happened

┌──[root@vms99.liruilongs.github.io]-[~]
└─$cat lock_demo.py
import threading
import time

lock = threading.Lock()

def worker(id):
    print(f"Worker {id} started")
    with lock:
        print(f"Worker {id} acquired lock")
        time.sleep(2)  # 模拟长时间的计算或 I/O
    print(f"Worker {id} released lock")

threads = []
for i in range(5):
    t = threading.Thread(target=worker, args=(i,))
    threads.append(t)
    t.start()

for t in threads:
    t.join()

print("All workers finished")

threadsnoop

┌──[root@vms99.liruilongs.github.io]-[~]
└─$threadsnoop
TIME(ms)   PID     COMM             FUNC
0          51671   b'python3'       b'[unknown]'
0          51671   b'python3'       b'[unknown]'
0          51671   b'python3'       b'[unknown]'
0          51671   b'python3'       b'[unknown]'
0          51671   b'python3'       b'[unknown]'

offcputime

┌──[root@vms99.liruilongs.github.io]-[~/FlameGraph]
└─$offcputime  -p pgrep -f lock_demo.py
Tracing off-CPU time (us) of PID 51397 by user + kernel stack... Hit Ctrl-C to end.
^C
    .......................
    finish_task_switch
    __sched_text_start
    schedule
    futex_wait_queue_me
    futex_wait
    do_futex
    __x64_sys_futex
    do_syscall_64
    entry_SYSCALL_64_after_hwframe
    [unknown]
    -                python3 (51402)
        157

    finish_task_switch
    __sched_text_start
    schedule
    futex_wait_queue_me
    futex_wait
    do_futex
    __x64_sys_futex
    do_syscall_64
    entry_SYSCALL_64_after_hwframe
    [unknown]
    -                python3 (51400)
        213

    finish_task_switch
    __sched_text_start
    schedule
    futex_wait_queue_me
    futex_wait
    do_futex
    __x64_sys_futex
    do_syscall_64
    entry_SYSCALL_64_after_hwframe
    [unknown]
    -                python3 (51397)
        267

    finish_task_switch
    __sched_text_start
    schedule
    do_nanosleep
    hrtimer_nanosleep
    common_nsleep_timens
    __x64_sys_clock_nanosleep
    do_syscall_64
    entry_SYSCALL_64_after_hwframe
    [unknown]
    [unknown]
    -                python3 (51400)
        2002609

    finish_task_switch
    __sched_text_start
    schedule
    do_nanosleep
    hrtimer_nanosleep
    common_nsleep_timens
    __x64_sys_clock_nanosleep
    do_syscall_64
    entry_SYSCALL_64_after_hwframe
    [unknown]
    [unknown]
    -                python3 (51402)
        2003178
..................
┌──[root@vms99.liruilongs.github.io]-[~/FlameGraph]
└─$

Any help will be greatly appreciated, best wishes